While we were near the Headmaster's office, we walked quickly. But before long we slowed down. By and by our heavy feet came to a complete stop. Sherlock put down the sword and tore the duct-tape off his hand with a ripping sound. He held the little silver bottle up in the air and swirled it gently, watching the contents shimmer and whirl in the shaft of light from an arrow-slit.

"A pretty little thing, isn't it?" he mused. "You would never know, to look at it, what it holds." There was a sudden spasm of his hand, as if he yearned to throw it away, smash it on the floor, let its shameful, black knowledge be lost in the dust.

"Do we have the right to give that to him?" I asked.

"Do we have the right to keep it from him?" asked Sherlock.

"It's a death sentence."

"It is."

"Sherlock, I know that none of the wizards think it's a good idea..."

"Because it's not." he interrupted.

"... but what if we did just kill Riddle as is?"

"Then he'll come back."

"Yes, but what if he didn't? What if ... we so completely destroyed his organisation that there was nobody left to help him return? He wouldn't technically be dead but ..."

"But be unable to come back in the sense which would render him a politically dangerous entity." Sherlock's voice had sunk very low. "'A mere spirit of malice that gnaws itself in the shadows, but cannot again grow or take shape'."

It took me a moment to place this.

"I didn't know you'd read Tolkien." I said after a minute

"Of course I have."

He fell silent again, gazing away into the distance. Through the arrow-slit we could see a glimpse of forest. There was a flash of something dark, as some flying creature swooped past.

"Harry's life, Sherlock."

"And what if it was you, John?" said Sherlock softly. "Would you have me keep this from you?"

I was silent.

"See? You would not. ... And neither would I. ... And we both know that Harry wouldn't either."

He stopped again, gazing quietly at the softly glowing bottle.

"No. We both know that wouldn't suffice. Even if the Death Eaters were to be utterly wiped out, there would always be people who would seek the same things as Riddle, who would bring him back to help them accomplish them. The man who nearly brought him back five years ago was unrelated to the original movement. ... And Riddle can still do terrible things in the spectre state. Reports have come back from Albania. ... Do as you would be done by, John. I have to give it to him."

A dog howled in the distance.

"And besides – I did give my word."

"What exactly did you promise?" I asked.

"To tell him anything I find which might help him defeat Riddle; to hide nothing – nothing which could possibly aid him in his task. I asked him how to help him, and he did not ask me to save his life, he asked me to defeat the sorcerer, no matter what the cost would be for him. ... I know, it does seem like betrayal, doesn't it?"

"It does."

"But wouldn't it be a worse betrayal to hide it from him?"

Suddenly Sherlock's manner of brooding reverie snapped. He snatched up the sword from the ground.

"John, bring the pensieve." And he dashed down the corridor out onto the battlements.

"The what?" I asked as I followed.

"That thing you're carrying." he said, setting down the sword and taking the bowl. "Don't cut yourself on the sword. You'd be dead in under a minute." He placed the bowl on the broad ledge and uncapped the little bottle.

"Do you know what you're doing?" I asked.

"Vaguely. Harry's told me about this."

"And you think you can operate it?"

"I don't see why not. It can't be too hard. The first time Harry did it, it was by accident. I want to know exactly what it is that I'm giving to him."

He poured the contents out into the bowl. Strangely, they did not splash and then grow still. Instead, they began to swirl, very fast indeed. Now, spread out on the bottom of the bowl, the substance no longer seemed evenly pearly, lighter and darker sections appeared, glimpses of things, as if seen out of a dream. I was certain I saw a glimpse of an old man, tall and bearded, in the same silly sort of hat that Sherlock was wearing. Only, it didn't look silly on the old man.

I turned to Sherlock. He wasn't there.

"Sher!..." I spun around, looking. There was no sign of him; not along the battlements, not back down the corridor, not on the nearest stairwell. I looked back towards the basin on the ledge. It occurred to me that it was really rather precariously situated.

"I don't like this." I said aloud. But nobody answered.

So I leaned against the battlements to wait for him, within arm's reach of the basin, but not so near that I might accidentally bump it and send it toppling down to the grassy lawn fathoms and fathoms below. The sun was rising towards noon. The day had become very warm. The lawns swept away from the castle wall, ending in dark woods, rich in their summer garb, and at the edge of water. A narrow lane, either paved, or made of stone so flawlessly laid as to appear seamless from a distance, wound away through the grounds. Outside the castle, on the lawns, was a number of what were quite unmistakably greenhouses, and garden beds surrounding them. Away by the edge of the forest, there seemed to be a little cabin. Smoke curled up from it, even though it was summer. Everything was well kept, orderly, and beautiful. But in all the vast expanse which lay open to my eyes, there was no sign of human presence. There was movement and sound everywhere; the rippling of the loch and the quiet sound of its waves, the faint unceasing movement of the trees, the calls of the birds, and their dark shapes, swooping in front of the sun. Something larger was flying down around the treetops (it was enormous whatever it was). A dog was barking. The breeze whistled around the castle turrets. But none of this was human. The castle, the grounds, lay almost empty, awaiting the return of the school year.

I was startled out of the gloomy train of thought this reflection brought on by the sudden realization that Sherlock was standing beside me again. His breathing was fast, and he was muttering very rapidly under his breath.

"Voldemort." he was saying. "Why? ... Why Voldemort? ... It's necessary that it happens beforebut, why ... Oh!" He nearly jumped. "That is insane! That is ridiculous! But then so is this whole preposterous affair!" With every sign of eagerness, he grabbed the pensieve, full though it was, and rushed down the corridor and into the stairwell.

"Sherlock!" I snatched up the sword and followed. "You were procrastinating a minute ago! What happened?!"

He spun on the stair and looked back up at me, his eyes shining.

"Snape didn't tell us everything Dumbledore said. Obviously he didn't think to attach any great importance to it, and since he was sending Harry the message through this" he indicated the shimmering basin "and not really through me, it didn't occur to him to mention it to us."

"Mention what?"

"Dumbledore insists that it must happen at Voldemort's hand! His and no other's. ... Does that not seem highly suggestive to you? ... No? Merely appalling? ... Well, perhaps I am mistaken. But no! I am sure I am not! Why else could it be so very vital? Essential, he called it; essential. Of course, it was really the only way to handle the affair all along, what with our intention to accost Riddle in open battle anyhow. But I don't see any good reason why it should matter from the point of view of the horcrux and if it doesn't matter to the horcrux then ..."

Sherlock broke off, and would have rushed on again, but I called him back.

"Sherlock, has it occurred to you that maybe we've just been wrong! Wrong, wrong, wrong all this time about trusting Dumbledore!"

"Yes, of course it has – did long since. But the theory stood up to no scrutiny and I dismissed it."

"Well have you any idea what that means subjecting Harry to? We know the man is a bloody psychopath! We know what he's already done to Harry. Does Dumbledore – did Dumbledore – want to hurt the poor kid as much as possible?"

"No. No, not as much but as little as possible. As absolutely little as could possibly be helped."

"Well then why?!"

"Well don't you..." he broke off for a minute. "Oh never mind. I can't say for certain, and you'd say I was out of my mind. Maybe I am – thinking such things. But..."

A glimmering light was rippling up the stairwell towards us. I recognized the silvery, warm aura of a patronus. But this one was one I'd never seen before. It was long and lean, running low to the ground so that it almost looked like a streamer flowing up the stairs. It took me a moment to discern where the sinuous body ended and the head and the tail began. When I did I thought at first that it looked rather like a weasel, and thought bizarrely of Ron Weasley. But it was too large for that, it was more like an otter; a sleek, svelte English river otter. As it reached Sherlock it stopped, and rose up on his hind legs, webbed forepaws folded before it, with its face, practically an extension of it's lean body, looking up to him. It spoke in the sweet voice of Hermione Granger.

"Riddle is coming, Mr. Holmes. Nagini is with him. He's checked the Gaunt house, and he's heading for the cave. He'll be on his way here very soon."

The silver otter faded away, leaving Sherlock and I alone again. He gazed at the place where it had disappeared with a decidedly doleful expression.

"I wonder if she'll ever forgive herself for ..."

He didn't finish. He turned away from where it had disappeared, and held the basin with one hand, while pulling Harry's marvellous map out of his jacket pocket with the other. "The 'charms' teacher is on the fifth floor." he announced. "But there's no one on the sixth and we're the only people on the seventh ... or between the sixth and seventh, technically, since we're on the staircase. Another of the professors is in the top of one of the towers off that way, but I understand she doesn't leave it very often. ... Someone called ... the 'Bloody Baron' is in the astronomy tower off that way, but he seems to be pacing back and forth. You probably won't have to worry about him. Snape's still in his office in the tower down the hall of course, but he'll be there for a while yet. John, I need you to stay here."

"Here?"

"Well not right here, obviously. This is the clear route up from the main entry. No, stay clear of right here. The last thing you want to do is run into Riddle all by yourself while we're all down in the lower levels. It would do no one any kind of good at all. But I need you on this floor. Stay off the main routes, and stay out of the Room of Requirement."

"And what am I to do?"

"You're to be on call. When you're needed, I dare say it'll be obvious enough. Stay within the distance a raised voice can carry from the room. That shouldn't be too hard considering all those little side passages nearby." He hesitated. "Unless ... unless you would be willing to take this to Harry yourself?"

I stopped, looking down at the shimmering pensieve. It glowed eerily in Sherlock's hands. He looked up and stared me in the face.

"No, no, never mind, John. You needn't answer that."

No. If ... if it has to be done. ... But Sherlock ... do you really see any hope for Harry?"

Sherlock looked at me with a peculiar mixture of amusement and disappointment.

"Even if I did, to show it might destroy it."

"Then I can't do it."

"No. I guess you can't. ... Well, John," he had become strangely brisk and chipper, "I shall, I hope, see you later."

He shoved the map out of sight and continued down the stairs at a great pace. Just before he went out of sight he paused, looking back up. Then he, like the otter, disappeared.

I now draw swiftly to the end of this narrative, but as I do so, there is much that I cannot say. I was not there at the supreme moment of revelation when Harry Potter learned the doom which had been hanging over him since infancy. I do not know what words Sherlock Holmes found to impart to him that terrible knowledge, or how he explained to him the role played by the hated Professor Snape, or whether he said nothing and let the memory speak first. I do not know in what manner Harry received the knowledge, whether he accepted it with instant understanding, or was struck with disbelief. Knowing Harry, I should suspect the former. But I was not there. And I did not see the dispute that then arose between the detective and the wizard. The first I knew of it was when I turned a narrow corner, and there, as if it had been waiting for me, stood Harry's silver hart; tall, majestic, and utterly beautiful. It spoke in Harry's youthful tones, and addressed me.

"Dr. Watson, Mr. Holmes is frozen in the broom-cupboard on the second floor, just down the hall from the bathroom. He should be able to get out by himself in a minute. But I thought that somebody ought to know where he is."

It turned and cantered away.

"No. Wait ... Harry." I called, starting to follow it. But before it could reach the open doorway at the end of the hall, it flickered away and went out – like a candle that had been extinguished.

I saw why I had been stationed here. Sherlock had intended to accompany Harry on that last lonely journey to the Room of Requirement, ensuring at least one other combatant in that all important encounter. But Harry had prevented him. I knew him too well to suspect him of anything but the very kindest of motives towards my friend. But the group of us, all five, should have ambushed Riddle together. Perhaps Harry did not believe that Ron and Hermione would let him do what he was about to do. Clearly he did not think that the muggle detective should accompany him on such a mission. And so now Harry was going, alone, to face Riddle – as Sherlock had never intended that he should. I was here as Sherlock's back-up. My place was now by Harry's side.

Before the light of his patronus had been snuffed out, I was running, swiftly as I could, straight for the Room of Requirement. The main corridor on the seventh floor corridor was empty. There was no sound save the troll tapestry flapping in the wind from the casements. The door to the room was open. I hurried along the corridor, my heart in my mouth. Then a voice, a high, cruel voice, raised in mirthless triumph, cried out from beyond the door. I recognized the incantation that it spoke; it echoed through the wide halls.

"Avada Kedavra!"

And then utter silence.

For a moment I stood, in realization of what had just happened; then I ran on, though the high doors and into the room of chaos.

Sick at heart, I jogged up and down the aisles of junk. The thingamajigs I had noticed before whizzed over my head. Their humming and the pounding of my feet and heart seemed to be the only sounds in the world – until I heard the unmistakable crack of someone teleporting. My hand clenched convulsively on the handle of Gryffindor's sword.

And then I saw what looked at first like a bunch of black robes thrown down in a heap on the worn and dusty floor.

Harry Potter lay on his back, his limbs thrown awry and his glasses half slipped off. There was no weapon in his hands. There was no mark upon his person. If I had seen one, I might have hoped. The killing curse – the mark-less spell which had killed poor Amelia Bones, and Sirius Black, and Harry's own parents, and so many countless others had now taken him too. Sherlock's wild hopes, whatever they had been, had been in error. He had sent our poor young friend to his death, as he had so feared to do. 'The Boy Who Lived' lay silent on the ground. He had come unarmed, unresisting, to meet the bloody hunter who had pursued him from infancy, and died – to ensure that others could live. From his face, he could have been asleep.

Tears blurred my eyes. They would fall, though I tried to blink them back. The mute appeal of the murdered youth on the ground struck into my heart in shafts of grief, and guilt, and fury.

And the monster had fled! I turned in anger. Where was the man who'd struck him down?! My view was blocked on either hand by the rows and ridges of worthless junk, but I had no doubt that it was he whom I had heard teleporting. That he could have found a way to teleport in this place did not surprise me at all. Failed, failed on both counts. Harry Potter lay dead, and Thomas Riddle had eluded us. I had been too slow. I should have been there with Harry, not after him.

With a curse, I bellowed for the monster to appear. But there was no answering voice or sound and I did not expect it. Riddle had escaped us for now. But not for long. There was only the one horcrux left him now. We would hunt him down if he fled to the ends of the earth! Thomas Riddle, born to end a thousand lives. How many more, now? How many?

"Would that the monster had not fled!" I cried aloud.

I turned back to Harry, still lying as he fell. I would compose the body, he should not lie thus, and search the room, just to be certain, before going and making sure Sherlock was out of the cupboard and telling him of my failure. We would then go and reveal to Hermione and Ron what had happened, and if their wrath allowed us, we could the four of us go and continue the hunt ... for however long it took. But before I had touched the boy, there was a pattering of feet.

For a moment I thought the diminutive, large-eared, wrinkled, little brown person who peered curiously around the cardboard box was Harry's 'Creature'. But a second glance assured me that this was an entirely separate individual; an individual eccentrically dressed in striped shorts, red suspenders, a blue bolero, several knitted caps, and one striped sock, ugly in the almost-cute way that a toad is, with big, round, sensitive eyes. He took one look, and a strange, strangled sound escaped him. Then with a horrible wail of anguish he launched himself upon the body.

"Harry Potter, Sir!" he cried. "Harry Potter! ... Harry Potter should not ... back! ... not when he-who-must-not-be-named ..." It was hard to follow the broken wails. "... freed Dobby! ... defeated ..." Whatever else it was the brownie said, it was lost in incoherent sobbing.

I stood there for a minute, appalled and and further grieved by this torrent of misery. And then I turned sorrowfully away to commence my search of the room, leaving Harry to his bereaved little friend. As I did so, I caught a sudden movement out of the corner of my eye, a furtive, silent movement.

From of a pile of old umbrellas, beer bottles, and coal hods, there rose the enormous, gleaming, triangular head of a massive snake. It was not nearly so large as the basilisk which Harry had slain, but it was by far the largest living specimen of its kind which I had ever seen. It's long forked tongue slipped out between its fangs and there was a soft sound like a heating pot. It rose higher, bringing more of its great length into view. It was coiling, coiling for the spring.

I could have quickly reached for the gun on my hip. But the sword was in my hand. That great stretch of sinuous body presented a better target to a blade than to a bullet. As the great snake lashed forward I leapt to meet it. The sword of Gryffindor clove the head from the servant of Slytherin.

Blood spattered me across the face, and I staggered backward from a blow to the chest. The mighty coils were thrashing madly in the narrow aisle, as the muscles and nerves of the dead serpent beat out their remaining energy. Stacks went flying. The sword was wrenched out of my hand. The brownie squealed. I was outright knocked from my feet and only narrowly avoid falling on the dropped sword. As the violent convulsions gave way to mere shuddering I scrambled to my feet, bruised, abraded, and panting; wet with blood.

Dust filled the air. The stacks which made up the sides of the aisles had been smashed and knocked about. A great coil of the body lay over Harry. The brownie was sitting up some ways off where it had been hurled by the snake's death throes. It was shaking its tear and blood stained face slowly from side to side as though trying to be sure which way was up. I thought I'd never seen anything more terribly pathetic in my life.

I bent down and dragged the snake off Harry. You could not tell now, that he had fallen by the instantaneous, mark-less weapon of the sorcerer. It looked as though he had been cut down in a battle and trampled underfoot. His glasses lay broken on the ground beside him. I picked them up and reached to wipe some of Nagini's blood from his face.

A clattering startled me and I started to a standing position. There, not ten feet away from me, standing on the other side of the umbrellas, stood the sorcerer, the devil-man, the thorn long twisting in Britain's side – Lord Voldemort. I cannot describe to you that face. Mere exposition of its pallor, its deformity, could never give its true effect. It will haunt my dreams for life. What is more horrifying than a thing which used to be human?

A smile played on thin, pale lips. Red eyes were narrowed thoughtfully. It seemed to be laughing softly to itself. Between long, sharp nails, it languidly twirled a old and gnarled wand.

"Avada Ke..."

Bang!

For a moment it hung there in mid-air, the mark of my bullet scarlet on its white forehead. I did not wait to see it fall; there was a sudden noise, and feeling of movement at my feet. I looked down.

Into the startled face of Harry Potter.

I suppose there must have been a crash as the body of Thomas Riddle fell to the ground among the coal hods and beer bottles. I did not hear it. I was staring in wonder and delight and blessed relief at the bruised and bloody but very much alive young man who was trying to gently disentangle himself from the frantic embraces of the devoted brownie, who had – with another great cry of "Harry Potter!" – hurled himself about his neck, still sobbing hysterically.

"Dobby! Ow! ... er, Dobby, you're strangling me."

"Dobby thought Harry Potter was dead, Sir! He thought that he-who-must-not-be-named had killed him, Sir! But Dobby should have known! Harry Potter is too great and too good to be killed by him!"

"Er, no, that's not what ..."

"And now Harry Potter and his friends have destroyed him!"

It was some moments before the ecstasy of little Dobby could be contained to the point where Harry could get a full sentence in edgewise. When he was finally able to, he recalled Dobby and I – both quite distracted with delight – to the necessity of investigating and making sure Riddle was really dead.

He was very dead. A grim figure the old murderer made amid the dust and blood, his distorted face gazed upward at the vaulted ceiling with a look of mild surprise. I did not know why, but it seemed from the marks on the filthy floor that when Harry had fallen Riddle had as well, and had been lying unconscious and out of view the whole time. Though still hideous, with animation and the power of breath gone, gone too was the fearfulness of the figure. Now that it made no claim to be a living man, it held no more terror than a gruesome and repulsive mannequin – a toy to frighten children on Halloween. So ended Lord Voldemort.

Dobby squealed with glee and jumped in the air, hopping and dancing about. His hats were all lost. And his bolero was ripped. But a greater picture of comical merriment could not be imagined.

"Harry," I asked, "how can it be that you are still alive?"

Harry turned to me. He was a dreadful mess; bloody and dusty and he looked rather odd to me without his glasses. But he was strangely radiant.

"You know about the enchantment my mother cast?" he asked.

"Yes, but ..." I stumbled, "how can that ... I thought that Riddle had destroyed Lily's enchantment?"

"No – he meant to. Well, he meant to steal it really. But he didn't really understand how that magic worked. ... I'm not sure how to explain it to a muggle ..."

"No, really, Harry, try me."

"It'll take some time to explain." said Harry. "And we need to let everybody know what's happened. But..."

Suddenly I remembered Sherlock Holmes, lying paralysed in the dark broom-cupboard, not knowing what was happening, unable to find out, unable to help, unable to call for help, unable to take any action whatsoever, unable even to drum his fingers in anxiety. Just waiting, waiting.

"And we've got to get Sherlock out of the cupboard."

"Oh. You're right, he must still be frozen." said Harry. "I hadn't counted on that. I'll have to find my wand first. I dropped it after I sent you the patronus, and I'll have to open the door with magic, since I locked the keys inside."

"So, you locked the door to keep others out?" I said as we turned away. "Not to keep Sherlock in?"

"Yeah, I didn't want Filch, the caretaker, happening across him."

"But if it can still be magically unlocked ..."

"Filch can't do magic. He'd have to go and get somebody else to open it for him, and I didn't expect Sherlock would be frozen long enough for that. I'd planned for him to have unfrozen by now and gone for Ron and Hermione."

"Where are Ron and Hermione?"

"Probably still back in the bathroom. ... Well, by now they've probably started looking for us. They're more likely to look down there first. When Sherlock and I didn't come back they probably though we'd just run into some kind of trouble right around there."

"Sherlock was going to come with you wasn't he?"

"Yes, he was."

Harry suddenly stopped; his eyes wide.

"He left you up here on purpose so you could take over for him if I prevented him from coming, didn't he?"

"I think so – though he didn't tell me that in so many words. I thought we were all going to ambush Riddle together. He toyed with the idea of sending me down to talk to you instead ..."

"Oh..." said Harry. "I thought he was only being ... That's why he was so insistent!"

And the boy took off at a run.

Suddenly, the cathedral space was rent by a terrible screech. It was a woman's voice. It started low and almost guttural, and went up high, wavering horribly, but not diminishing. There was hatred, and grief, and unappeasable fury in that cry – ringing on and on until the walls reverberated with the dreadful sound.

Harry looked back over his shoulder at me.

"It's Bellatrix Lestrange."

Somehow, she knew where we were. Things started blowing up. Entire columns went flying. We made it to the door – only narrowly avoiding a rusty pot-bellied stove that came flying out after us – and tore down the corridor. A blast of green light flashed past us and I spun around; there was no cover here, not for us, but not for her either. For a fraction of a second, as I pulled the trigger, I saw a glimpse of a ravening mad-woman, eyes blazing, nostrils flaring, chaotic black ringlets streaming, lips pulled back snarling, before a big dark mass crashed into her. There was a great resonant humming.

A rotten old grand piano, painted garishly in a sort of hot purple and newly adorned with a bullet-hole, was sitting upside down on the corridor floor, coasters spinning. Dobby trotted out of the Room of Requirement.

"Did it hit her, Harry Potter?" he asked.

"It fell on her, Dobby." said Harry. "I think you've killed her."

Dobby started in shock

"Dobby didn't mean to kill!" he cried. "He only meant to maim! She was trying to hurt Harry Potter!"

Her skull had been crushed by the blow. In spite of the cruel and barbarous deeds for which the woman had been renowned, Dobby seemed horrified that he'd actually killed her.

"I wonder what she was doing in Hogwarts." said Harry. "She wasn't here when we came. Dobby, we need to tell the Order that Riddle's dead but there may be other Death Eaters showing up. Can you go down to the girl's bathroom on the second floor and see if Ron and Hermione are there? Tell them that he's dead, and ask them to send for the Order?"

"Yes, Harry Potter Sir!"

The brownie spun round and disappeared with a crack. It had been he whom I had heard teleporting. With this information came a cold, sinking feeling, like a bad memory does when you suddenly recall it. For a moment I was engaged in trying to remember what was so terrible. ... As the icy chill started biting into my flesh, I remembered the stone path through the tangled thickets.

"Harry."

He stood up. His eyes widened in horror, fixed on something which I could not see.

"Run." he said.

Together we tore down the corridor; formless terror behind. We had come in sight of the stairwell when Harry abruptly stopped. I knew from the look on his face that we were surrounded.

The sunlight was blotted out. My ears were filled with the cries of men long gone. I could see nothing at which to shoot. In frantic desperation I swung the sword of Gryffindor fruitlessly in the empty air with arms scarcely able still to wield it. I knew that in moments they would be able to no longer. The thoughts and sensations I had been trying to hold back, to keep at bay, for many hours, were bursting their dam, coursing through my mind and body like poison, numbing my limbs, darkening my eyes, paralysing my mind with horror.

"John," I heard Harry say in a frighteningly breathless voice as we stumbled down the corridor, "that's not gonna work. Try to think of something good ... something to be glad about ... something happy."

Glad. And for a moment, the small part of my mind which was still my own laughed in sudden realization of the true absurdity of the things going on in my head. Happy? I saw, even if only for a moment, that the despair was truly a fraud. It did not come from within; from the state of my own heart. Even less did it come from without; from the actual state of the world. It reflected no realities whatsoever. It was sheer illusion. Give in to it? Now? Now at the very moment when it had been in reality defeated? We had won. Harry was here, alive beside me; I had not killed him, nor contributed to his death. The blood of the innocent was unspilt. And the murderer, the necromancer, was gone, him and his devices of sorcery – gone like a twisted dream. I owe Harry Potter much thanks for that advice. It gave me strength and sanity to hold out just a little longer, not surrendering to the unspeakable black despair. But oh, how fragile a thing is objective knowledge in the human mind. The most perfect truth, known with utter certitude, can be so easily swamped by unreasoned waves of groundless emotion.

My knees hit the ice cold floor. I did know where Harry was. I was alone in the dark.

It looked at first like a tiny, glowing ball, bouncing merrily along the ground towards me through the dark haze. The shadows did not flee and disappear, but they seemed to recede away from it. I knew immediately that it was a patronus; smaller than any I had yet seen It could be nothing else. It bounded right up to us, an indistinct little bundle of shimmering light, bringing warmth and little glimmers of sweet rationality with it. It sailed over my head, and a ray of sunshine seemed to fall. It bounced to the right, and it bounced to the left, and it skittered round about us, a little gleam of silver in the black.

Then my attention was diverted, for Harry was struggling to his knees. He lifted his dark, unruly head and opened his vivid green eyes. From his upraised hand, light burst forth.

It blazed, and it shone; bright silvery radiance, surrounding us both, washing the chill from the air and the blackness from our minds. The shadows fled before it. As it grew and surged after, I caught glimpse, an ethereal hint, of hooved legs, and a majestic antlered head.

The bouncy-ball turned to follow the hart, and as it did I saw it clearly for the first time, the rounded prickly body, the tiny legs, the pointed little snout. It was a hedgehog.

As the warm, yellow daylight returned to the corridor, Harry and I got back to our feet

"Whose patronus was that?" I asked.

"For a moment, I thought it was yours." said Harry.

"I'm a muggle!"

"Yeah, so it can't be that."

"Is Ron's patronus a hedgehog?"

"No, it's a terrier."

"Well, who has a hedgehog patronus?"

"I dunno." said Harry. "... Maybe ... Snape?"

Somehow I had difficulty imagining the grim, sardonic professor casting that patronus. I could have sworn that it was not he. There had been something indefinably familiar about it.

"Well never mind for now." he continued. "I've got to go tell Sherlock we haven't ... "

A woman's voice cut him off.

"John? ... John!"

"Mary?"

I turned in surprise.

She wielded a wand in her right hand. Sweeping robes of palest blue were gathered at her waist with a girdle of silver. Her face was shadowed by a wide brimmed, pointed hat of of soft grey. But it was unquestionably my Mary. She was rushing toward me, alarm in her face.

"John, you're not hurt?!" she cried.

I have mentioned that Harry looked as though a battle had passed over him, and I can hardly have looked far better. We were both plastered in slime from the Chamber of Secrets, drenched in blood from the python, and covered in dust from the Room of Requirement. And I was missing most of my buttons.

"No, no. It's not my blood," I said, "or most of it's not. I'm fine, everything's fine. In fact, it's wonderful, Mary. Mary! However do you come to be here?! I thought I left you safe in London!"

There was a crack as Dobby reappeared. Mary was distracted for a moment, but then turned back to me.

"Mycroft Holmes didn't quite trust the five of you to send help quick enough. The strike-team is on its way. I set off the flare as soon as I saw those awful things! John, we have to..."

"Wait ... the dementors? You actually saw the dementors?"

"Mm-hm."

"I mean ... you can see them?"

I glanced down at the slender hand on my shoulder, and the twig-like tool clasped firmly in the strong little fingers.

"Harry!"

"Harry."

Ron and Hermione's cries of greeting to their friend fell upon my ears, but I didn't turn to see them.

"Mary, why didn't you tell me?!"

"What?"

"Where'd you get that?"

"This? Sherlock gave it to me!"

"Sherlock gave you a wand?!"

"Yes, well, I don't think he meant me to keep it. I think he probably nicked it from somebody."

"But, the patronus was yours? You sent us the patronus?"

"I didn't know Harry was with you."

"But ... you're a wizard, Mary?"

She stopped; her jaw dropped. In a small voice, she said:

"So that's what they are."

There was a sudden thundering of feet, not like the quiet pattering of Dobby or the thumping of Ron and Hermione. Thinking that we were discovered, I spun round and reached for my handgun. But I had no need to draw it, for it was the flame-headed Weasley Twins who dashed round the corner. And following behind them was their kindly father, and Remus Lupin with his wife, and many others who we had left behind in London that morning, members of the Order of the Phoenix and younger people from Dumbledore's Army. The strike-team had come. They must have landed on the astronomy tower, and come down expecting to find battle. Finding us there, with no enemies in sight, they stopped in surprise. The trio rushed to them, explaining in three tongues what had happened. I turned back to Mary again.

"He knew!" I exclaimed, laughing. "He knew that my wife was a wizard and he didn't bother to tell me!"

"Well, he didn't tell me about it either, so don't feel picked on, dear." she said. "I really should have realized it myself, I suppose."

But we both knew why Sherlock Holmes had not told either of us. He knew Mary's indefatigable curiosity. The past year had been a very dangerous time for a muggle-born wizard to become curious about the British Wizarding world.

A hundred things were resolving themselves. Of course neither of us had recognized the link between Mary and the wizards. The bright paraphernalia of their culture, the curious vocabulary of their dialect, the remarkable technology of their secret world, had all camouflaged it. What had all that to do with Mary's quiet, penetrating intuition, her wonderful way with small creatures, and the healing in her fingers. I suspected now that her abilities had gone farther than she had ever openly shared with me. I suddenly realized that she had, without the paintbrush, been casting patronuses ever since I had known her. No wonder her first attempt with a wand had been so beautiful. She'd always known how.

"John," she said, cutting into my train of thought, "we've got to go. Sherlock's in some kind of trouble."

"What?! How do you know?"

"I heard him. I heard as soon as I set foot in the castle, but I had to find you first. Why isn't he with the rest of you?"

"Because Harry locked him in a broom cupboard, trying to protect him from himself! Harry!"

"Oh." said Mary. "I see."

Harry was stuck in the middle of the Order, explaining something.

"Oh, never mind. We'll find him. Let's go." I grabbed Mary's hand and ran past the Order for the stairs, my mind filled with images of what could be happening to Sherlock Holmes. "You shouldn't have come to me. I was only dealing with dementors. You should have just sent the patronus and gone to help Sherlock."

"No, no, no, I think I know what's wrong with him now." Mary said, her voice quite calm.

"What? What was he calling, Mary?!"

"Not was. I hear him now."

I stopped for a second at the top of the stairs. But I heard nothing. She was listening to a soundless cry.

"John dear, lock Sherlock Holmes in a cupboard while something like this is being decided right above his head and what do you expect..."

A cold and demanding voice interrupted her.

"Watson! What is the meaning of this?"

Standing rather unsteadily in the middle of the corridor, arms akimbo and face set in a scowl, was the Headmaster.

Lupin looked up. As his eyes fell on the grim figure, something happened to his pleasant, reasonable face; it became nearly unrecognisable, wild and raging, wolfish almost in it's ferocity. With a cry of rage, he seized his wand.

"Wait, hold it!"

"Remus, no!"

I and Harry had called out together, both jumping in front of the scowling headmaster. It is difficult to say whether the Order members or the headmaster himself looked more shocked at Harry's behaviour. Somehow he (and I with him) had found himself in the extraordinary position ofdefending Severus Snape.

"Harry, whatever has come over you?" exclaimed Lupin in surprise.

"Uh, he's with us." said Harry.

"He iz dee murderer of Dumbledore!" cried Bill Weasley's platinum haired wife.

It a moment for Harry to make himself heard over the roars of fury from the strike-team. These people were the nearest things Snape had to even allies, and they were all clamouring for his blood.

"Snape's been acting on Dumbledore's orders all along!" cried Harry. "Even that night on the tower."

"Harry, you said yourself..."

"I was wrong! I was talking about it with Duh-er ... I was wrong. ... Dobby, show the Order what happened in the room of requirement. I'll explain about it later. Right now, there's something Ihave to do."

And Harry turned and ran. Mary and I were right with him. Ron and Hermione appeared out of the crowd and came along. A glance back showed Snape to hesitate, then follow after us, the Weasley Twins shadowing closely behind.

Led by Harry, we came down to the second floor very swiftly, taking several oddly placed shortcuts which I would never have guessed were there. The corridor was empty and bare; there was no sound of man behind the closed door that Harry led us to. He unlocked it with a silent spell, and it swung open on its hinges. Light flooded into the shadowy recess.

There, leaning rigidly against the wall amongst the mops and the brooms, was what looked to be a perfect waxwork image of Sherlock Holmes. His hands were held out before him, in an expressive, dearly familiar gesture of explanation and exhortation. His lips were slightly open, as if a word had just left them, or was just about to. His grey eyes were open wide, and intent in their fixation on the opposite wall. His head was bent slightly foreword. It was by far the most lifelike image I had ever seen of a man. ... But if I had not known better, I would have thought that it was only an image.

"Finite Incantantum."

It all changed instantly. There was a slipping, and a stomping, and a grasping of Harry's outstretched arm, and Sherlock Holmes, animate and expressive as ever, was standing there, looking over the eight of us, taking in with quick, discerning glances the state of the company crowded round the door.

"Ah." he said. "So we've won then."