Moving through the smoke and chaos, feeling bits of glass whistle past your ear, watching the sparks hiss and fizzle in the puddles – it was like being part of the orchestra again. Each shout, each explosion, each crack of falling timber, was a different instrument, and they harmonized so well that Jack was feeling exceedingly proud of himself by the time he sauntered down Holywell Street.

It wasn't quite like it had been in India, though. He wasn't part of the music anymore. But, because he knew every note, he could move inside it – ride the swells and dips and crescendos, use the thunderous percussion to drive off any obstacles that threatened to bar his way. He knew the schedule so well that he could cue the explosions with a wave of his hand. He could step out of the way of falling debris as effortlessly as if he were sleep-walking.

He felt like two people now: the one that was calm and reasonable and gave out orders, and the one that thumped the wall, or tore up floorboards, or hyperventilated at the thought of going into the mortuary, where Ellini's body was lying, cold and lifeless, on a slab.

He also suspected his body was reacting to the sudden absence of the chemicals he had used to imbibe on a daily basis. Not only was he no longer taking Sergei's violence-suppressing wonder-drug, he had also given up alcohol, cocaine, tobacco and – hardest of all – opium.

He hadn't meant to forego any of them to begin with. But in the first few, excruciating hours after Ellini's death, he had lit up a cigarette out of sheer habit, and almost gagged on the associations.

He had devoured the cigarettes when he'd needed her, hadn't he? Whenever she let her hair down – or when her dress was clinging to her torso – or when she was smiling particularly adorably. Somehow, his old desires had been trying to work their way to the surface, but had come out as an unbearable craving for cigarettes.

And now he had the same needs, but the smoke only laid them bare, instead of covering them up. He knew what he was craving now, and how impossible it would be to get.

After that, giving up the other drugs had been a fairly obvious choice. He never wanted to feel that he wasn't in control of his actions again. He wanted to feel his own pain, his own hunger and his own desire, no matter how extreme they were. He was going to be himself, no matter how much he suffered for it.

So he was walking down Holywell Street, counting the seconds between blasts – counting anything that would allow him to stop thinking about Ellini for a few seconds – when he saw the unmistakable, bulky figure of Sam outlined against the flames of the old Ashmolean building.

And, at first, it was the building, rather than Sam, that attracted his attention. They had run over that rooftop together, hadn't they? He had held her up to help her reach the flagpole, and then she had come swinging down on her grapple, kicking the gargoyle off the roof and onto the cobbles below.

God, that had been a good night.

But a crunching of glass brought him back to reality, and he realized that Sam had seen him, and was striding across the melee towards him, incandescent with rage.

And it was bizarre. Even though the air was thick with smoke and noise – even though their faces were stained with firelight, and broken glass was crunching beneath their feet – his tone was so familiar and stern and irritable that it felt as though they were back in the world of three days ago, and Sam was taking him to task for some minor parole violation.

"Did you kill Miss Syal?" he shouted, gesturing wildly with his hands. "And the gargoyle, and the old man? And Violet Pike! Why Violet Pike? What has she got to do with anything? Did you blackmail the mayor? Do you have any idea of the trouble you've caused?"

"By killing three people?" said Jack, amazed at the way this conversation was going. "I didn't think it would pass without comment, if that's what you mean."

Sam stopped, as though suddenly realizing what he was saying. He fumbled in the pocket of his coat and pulled out a gun. It was so familiar that Jack wanted to burst out laughing. That ancient revolver he never loaded, because he was so horrified at the thought of taking another life. He never realized you could tell from the way he was holding it that it was far too light to contain bullets.

"Three people?" said Sam, raising the gun a little to get Jack's attention. "Which one didn't you kill?"

Jack rolled his eyes. "The one I couldn't kill. The gargoyle. Only the doctor's last descendant can kill the gargoyles, yes?"

"You did steal the Book of Woe!"

"I wanted to know everything," said Jack. "When you've spent the most crucial month of your life in a state of enforced ignorance, it's amazing the thirst for knowledge you have when you wake up."

Sam glared at him. "Oh, please! As if you were a prisoner in your own body, watching the things you did with powerless despair! You were exactly the same man you've always been! You didn't do anything out of character. You're not even really doing anything out of character now!"

Jack winced at the phrase 'out of character'. She had said that, hadn't she? Last night, or the night before? All the nights were blurring into each other now. She had said that stabbing her in the chest hadn't been out of character for him – that everything she'd ever loved about him, she'd made up.

For a moment, the world lurched off-balance, and he was terrified that he was going to fall into the pain again. He could even see it – a sort of gathering dark at the edge of his vision, threatening to spill over everything like an upset bottle of ink. And he didn't know what he'd do if it took over. He might come round in a few seconds and find that he'd throttled Sam – or even some passing nobody who'd had nothing to do with Ellini's death. The anger needed a tight focus, or it would swallow him whole.

"Anyway," said Sam, who seemed to think he'd gained some kind of victory by causing Jack to stagger. "Alice said she didn't kill the gargoyle."

"What a remarkably perspicacious woman she is," said Jack, still with his eyes tight shut, still tasting the metallic tang of pain in his mouth. "In fact, she thinks that because she was unconscious at the time. After the old man chloroformed her, Ellini – who, incidentally, was bleeding to death on the floor at this point – wrapped Alice's hand around the knife and drove it into the gargoyle's heart."

He risked opening his eyes, and saw Sam looking fractionally less angry than he usually did. For some reason, it only intensified the bitter taste in Jack's mouth.

"Now that's doing something clever with a prophecy," he went on. "That's making necessity a virtue – or, even better, a weapon. It's just a shame it didn't do her any good."

"Why did you kill her?" said Sam quietly.

Jack shut his eyes again, before all the black ink could spill across his vision. "Well, I've asked myself that a few times, Sammy – in various different moods – and I think the only answer which doesn't get unnecessarily technical is that I am not a very nice person."

"You set fire to the Bodleian!" Sam shouted, as though to emphasize what an understatement this was.

"Oh, yes," said Jack earnestly. "It was wonderful. Even the hardened criminals winced."

"You've gone insane."

"I wholeheartedly agree with you. Do you know how you can tell? The further I get from rationality, the more long words I use. Oxford did that to me." He hesitated, and then said tentatively, "It'll happen to you too. Maybe when the Burgess inside you gets out."

Sam stared at him, and he gave a nervous, apologetic wave of his hand. "I should have said, I collect information about people. It's sort of a hobby. But, even if I didn't, I think I would have noticed something different about you after Burgess bit your neck. Watch your shadow the next time you get a few moments to yourself. I'm sure you'll-"

Sam interrupted him. "Did you do something to that woman with the perambulator on St Aldates?"

Jack burst out laughing, startled and delighted. "You know, I was so sure I wouldn't get any credit for that! I thought 'Sam's paranoid, but could he really be that paranoid? Enough to assume that I'd watch his eyes on his morning walks to work and notice the spring in his step after he passed that perfect stranger?' How many times do you think I would have had to watch you before I made that connection? Ten – twenty? Let's say a minimum of ten early mornings, standing concealed and following the direction of your gaze. Could anyone believe I'd be that bored, and that thorough?" He clapped his hands briskly. "I'm so pleased, Sammy. Your paranoia and my genius were made for each other."

He paused, because Sam was still glaring at him, breathing very heavily now.

"She's all right," he added hastily. "I've got her in a nice cellar – not too damp – and there's a nurse-maid taking care of the baby. Incidentally, you did well to never talk to her. She's got the most annoying voice I've ever heard – although I suppose nobody sounds at their best when they're hammering on a cellar door."

Sam raised the gun and took a slow, meaningful step towards him. "I'm arresting you for the murders of Ellini Syal, Violet Pike and-"

"It's not loaded," said Jack. And again, he couldn't help laughing, amazed at how easy it was – after all these years – to say. "It's never loaded. You keep the bullets locked in your desk-drawer at the station. You go out on duty every night with no bullets in your gun, because you never wanted to be responsible for another death, after that shop-girl."

He broke off and looked at Sam, who hadn't moved. It took an expert eye to see it, but the barrel of the gun was weaving around ever so slightly, as though it was being held with shaky hands.

"It's not a problem," said Jack. "It actually works very well. You never need to fire the gun – you wouldn't even need to aim it, if you knew your own power. Everyone's scared enough to do as you say anyway, without the threat of violence. But it's something I should have remembered before I sent you that arrow. How did I think you were going to kill me when I knew you were this desperate not to take another life?"

The words 'another life' made Sam's eyes narrow. He steadied the gun, still aiming it resolutely at Jack's chest.

"Are you sure? You don't think I might have changed my mind, under these circumstances? You don't think, after four murders and a riot, I might have decided to load my gun tonight?"

Jack smiled and took a few tentative steps forward. "Ye-es, I'm sure. But it wouldn't take a second to prove me wrong, would it?"

Sam lowered the gun and punched him in the face.

It could have been better. A man that big could have sent him flying backwards with a really well-executed punch. But, as it was, it was a nice distraction. A left hook to the jaw that sent him staggering to the side for a few moments, before he regained his balance. Jack raised a hand to his mouth, testing for blood.

"Here," he said suddenly, digging in the pockets of his coat for another gun. "This one's loaded. Colt single action army revolver. Much nicer than your standard-issue police guns."

He snapped the cylinder open to show Sam the bullets in the chambers, and then closed it again, holding the gun out to him, handle-first. "Maybe you could shoot me somewhere non-fatal but painful. That would probably suit your mood at the moment. Try the knee-caps. They can cause a world of trouble."

He raised his arm to the side and fired a shot into the smoke. It caused the dark shape that had been looming in his peripheral vision to fall forwards with a muffled groan.

"Oh, relax," he said, catching Sam's sudden intake of breath. "I'm good at shooting people non-fatally. I've had years of practice. Gleeson here's going to be fine, aren't you, Gleeson?"

He gave the dark mound a nudge with his foot, and was slightly relieved to hear it groan again. He was never sure how much he could rely on his instincts these days. They were well-honed, but they also wanted to kill everyone.

"So how about it?" he said, advancing on Sam. "You've got five bullets left. That should be enough to cause me some inconvenience."

He held out the gun again, but Sam slapped it aside and kicked him in the crotch.

Jack, who'd been preparing himself to be shot, found, to his astonishment, that this hurt even more. There was an incomprehensible amount of pain – an unfair amount, given that he had no particular use for this part of his body anymore.

He dropped to his knees, barely aware of the confusion going on to his right. There were other policemen, maybe? Sam had dashed off into the smoke, blowing his whistle, and now there were others, talking in hushed voices, lifting something dark and floppy onto a stretcher.

Oh, he thought, through the fog of pain, it's Gleeson. Oh, bless him, he summoned reinforcements to take care of Gleeson, not to help him arrest me! How could I ever have thought he was going to kill me? He's a fucking school-teacher!

And now he'll send them away. He won't want anyone else to get hurt. He'll come back and try to reason with me. Maybe he'll even start hoping that I'll kill him and solve all his problems. But he must know I could never do that. If he's good for one thing, it's getting up. If even Burgess couldn't kill him, what chance would I have?

He's just like me, thought Jack, in the delirious clarity of agony. He wants to give up, but he can't. There's no reason to go on, but he must. We're exactly the same. The only difference is, I'm going to win. I have to.

The voices drew off into the smoke, and then there was just Sam, his shoulders slumped with gloom, coming to sit beside him on the curb.

"You think you can take me on by yourself, Sammie?" said Jack, still hanging his head, trying to fight off the pain.

"I don't want anyone else to get hurt."

Jack laughed. It was slightly high-pitched, but whether this was due to the delirium or the crotch-kicking, he couldn't be sure. "You're fighting a losing battle there, mate."

"You need help, Jack," said Sam, lighting up a cigarette with surprisingly steady fingers. The smell of the smoke made Jack's insides writhe with nausea, but he kept his jaw locked and said nothing.

"You've killed people," Sam went on. "That's never going to go away, do you understand? I know, because, as you were cruel enough to point out, I've killed someone too. In quite similar circumstances. I know..." He trailed off, but Jack felt the lurch of nausea again, as sharp and sudden as if he'd fallen off a cliff.

"I'm sorry, were you going to say you know how I feel?" There was hot anger rising up in his throat, blistering his tongue. "You spoilt little brat. Do you have any idea what I'd give to be you? Just for the little things? Just to have not killed your loved one with your own hands? Just for rape and torture and slavery to have nothing to do with it? Did someone make you treat your shop-girl the way you treated her? Did someone reach inside your head and take away all the things that make you you? Did she die slowly – in agony – hating you the whole time? Don't you dare – don't you dare – tell me you know how I feel! You do not know how I feel!"

The world suddenly swam back into focus. Dimly, he saw that he had grabbed Sam by the collar, pulled him to his feet and slammed him up against a wall. He was amazed that he'd even been able to move him. But perhaps he had co-operated – or at least hadn't fought back. For the first time since Jack had met him, his face was completely devoid of anger. He was looking horribly composed and aware – almost sympathetic.

"Save your sympathy for her," Jack spat.

"It is for her, you fucking idiot."

Jack took a deep, shuddering breath, and removed his hands from Sam's shirt-front. He even tried to smooth out some of the creases he'd made, but this was too much for Sam, who slapped his hand away angrily.

And it was magic. As soon as Sam was angry again, Jack found that he no longer had to be. Sam was shouldering the burden for both of them, just like he always had.

"You know, you're doing very well," said Jack, taking a courteous step backwards. "You called up reserves from the County Police Force – men I don't know, and didn't help to train. That was clever. You moved Alice and Sergei to the mortuary – smarter still. It's not going to make any difference but, just to show you I appreciate the effort, I'm going to give you this."

He fumbled in his pockets again, this time bringing out a crumpled sheet of paper, which Sam stared at, but didn't take.

"What is it?"

"My notes on you. Sorry they're a bit crumpled," said Jack, gesturing nervously with the paper. "I'm having trouble not breaking things at the moment."

Sam eventually gave in to his curiosity and snatched up the paper. Jack watched as he smoothed it out and ran his suspicious eyes over it. A lot of his writing was illegible, of course – or blotted-over with diagrams and ink-smudges. But Jack was fairly sure his eye would catch on certain phrases. 'Too angry to think clearly' would immediately leap out at him, as well as the short, suggestive question 'the biting kind?'

And when the colour drained from his face, Jack was certain it was because he had seen the phrase 'Lily's letters' scrawled at the bottom of the page, and circled heavily, as though it was the total in a lengthy calculation.

"It's worse than you think," said Jack softly.

"It couldn't possibly be-" Sam started, but Jack interrupted him, chuckling.

"Oh, no," he said. "Trust me. It can always get worse."

He yanked Sam to the side, so that a falling beam missed his shoulder, and went on, over the roar of the flames, "I'm coming for your prisoners. Sergei and Alice. At about eight o'clock tomorrow night." He nodded at the crumpled sheet of paper in Sam's hands. "Now you know when to expect me, and what I'll be using against you when I come. That's fair, isn't it? That should give you a fighting chance."

"Is it important to you that I have a fighting chance?" said Sam coldly.

"It's important that somebody fights me," said Jack, judiciously re-phrasing. "You have no idea how much I'd appreciate the distraction."