"Firstly," Will said. "You're immortal, yes?"

Magnus nodded. "Correct, yes."

"If you were cursed...and that curse said you would die, what would happen?"

The warlock leaned back, thinking. "I don't imagine much would happen, if I'm honest. But no, I don't think anything would happen. I can be killed, but not of old age. I heal, but I can be...shot, for example. But that is a supernatural force, and I have supernatural powers. And curses are usually cast by demons or other warlocks, and I think the caster would avoid attempting to curse a High Warlock, if I'm truthful."

Will nodded, reassured by this information. If he was going to confide in Magnus, he wanted to make sure his friendship would not bring the warlock to any harm. Will was cursed, and had long since given up looking for a cure. But there was another cure he would never stop looking for, one that might require magical assistance to find.

If Will was to tell Magnus about Jem, and how Will so badly did not want him to die, this might evoke Magnus's pity. Will didn't want that, but he knew that was the natural reaction to stories of woe. If Magnus felt bad for Will, even found himself liking Will, the shadowhunter had to be sure this wasn't at danger to the warlock. But, after what Magnus had said, it didn't seem like it would be...

"Is this what you wanted to ask me?" Magnus asked.

"No, but it was relevant." Will answered.

"So," Magnus said, resting his head back against the back of the armchair. "What did you want to talk to me about?"

"My parabatai, Jem, is dying." Will said bluntly, with the practised simplicity of someone who had said this sentence too many times. "He is the one with the silver hair." He added in clarification.

"Are you permitted to tell me what it is that is killing him?" Magnus asked.

"He is addicted to the drug Yin Fen." Will said. "He's dependent on it to live. But one of the properties of it is that it is toxic. It just buys him time, really. He can take the drug, and die slowly, or refrain from taking it and die quickly and painfully."

"Not an easy decision for anyone to make." Magnus said, half to himself. "Least of all a young man like Jem."

Will looked up, with a sudden and intense urge to explain.

"It isn't his fault." Will blurted. "Jem's, that is. He didn't get addicted to it because...it...a demon did it to him, a Greater Demon called Yanluo. It did it to torture his parents, to get revenge on them for killing its litter. It made his parents watch while it made tortured Jem. His parents died but he survived and now...I...I just wanted to tell you." Will trailed off. "It wasn't his fault. He's a victim."

"It's alright. I believe you. From what I've seen of your friend, he doesn't seem like the type. You don't have to defend him." Magnus said gently. "You're preaching to the converted, Will."

Will pulled up short. He wanted Magnus to help Jem recover, and he knew that to do that, he needed to provide as much information as he could. But Jem had never asked him to do this and whilst he was not exactly secretive about his illness, nor ashamed of it, he also didn't like to speak about it often. Will remembered, when Jem first arrived at the Institute, he had been hesitant to talk to anyone – even Will – about his sickness. Taking his medicine disgusted him, and Will remembered the first time Jem had ever been truly upset about his situation, or at least the first time he'd ever told Will.

"I hate it." Jem spat bitterly. "I hate all of it."

Will sat opposite his parabatai on the floor of Jem's bedroom. "Jem, you have to drink it." He said, as they both looked at the glass of Yin Fen-infused water.

At thirteen years old, Will already thought it his personal responsibility to take care of his friend. What Will didn't know was that Jem felt the same way about him, felt an obligation to repay Will's vigilant care with an attempt to subdue his reckless tendencies and stand beside him in situations from which Jem could not find a way to remove them both. And both boys felt the same; if their life was to be dedicated to watching over their best friend, for however long they remained side by side, so be it.

"It just...I just...I wish it hadn't happened. I want to go home." Jem trailed off quietly, pushing the heels of his hands against his closed eyes. "I know that shadowhunters are meant to be brave, but I just want to go home, to see my mother and father. I wish I'd never even arrived here."

"But then we never would have met." Will said. "We would never be parabatai."

Jem looked up and put his elbows on his knees, resting his chin on his hands. "That is true."

"Please drink it." Will persisted gently and Jem sighed, reaching for the glass. Will looked down to give Jem privacy, and when he heard the soft thud of the glass being laid, empty, back on the floor. Jem's eyes were glimmering, but he looked down, blinking and when his face turned back up to Will's, he seemed as composed as ever.

"Will, are you alright?"

Will looked up, Magnus's voice pulling him swiftly from his reverie.

"Is the demon still alive?" Magnus asked, for what had to be the third or fourth time, not that Will knew that. "Yanluo, that is. Or at least in this dimension."

"Oh, no." Will said. "It was sent back to its home dimension years ago."

"Slightly more complicated." Magnus said to himself. "But not impossible, of course. Rare is the impossible task."

Magnus liked to approach all aspects of life with something like controlled recklessness. He was drawn to inchoate ideas. Whilst he had little need for haste, with a life so long, what he did have little time for was worry. Why approach anything with anything less than complete abandon? Because really, if people weren't talking behind their hands about your choices, were they even worth making? So, in Magnus's mind, all Yanluo's banishment from this dimension meant was that he might have to search a little more.

"'Things deemed unlikely, e'en impossible, experience oft hath proved to be true'." Will said, and stood up. "Thank you, Magnus. How can I pay you for your assistance?"

"You should wait for my searches to prove fruitful." Magnus smiled. "If I do find anything, and I promise I shall try to, then we can discuss payment."

Will nodded. "Thank you."

Magnus watched from the drawing room window as Will set off down the streets, sunlight glinting off the buttons on his coat, glossing his hair in illumination. Yes, Magnus thought sadly to himself. I will definitely try to find a cure for Jem's illness. If for no other reason that, without his parabatai, Magnus didn't know how Will would be able to face the world. If only the boy could tell Magnus his story, because Will – the warlock could tell – was withholding something, something that was eating him alive from the inside out.

Jem, Ciel, Sebastian, and the Lightwoods had been ushered into the dining room to give the Institute's other wards – particularly Charlotte – all the information they'd gathered. Henry, Charlotte explained, was on the brink of completing a new and revolutionary device.

"He will be up to attend the meeting as soon as it is finished and working," she said, before adding quietly under her breath, "So, any time between now and sixty years time..."

It was perhaps fortunate Will was not here, Jem thought, hiding a smirk. He would have said the same thing, but far blunter and without bothering to lower his voice.

Jem explained their meeting with Ragnor and Magnus, and how they'd summoned the culprit – Camille Belcourt – with the sample. Charlotte, by this point, had a roll of parchment, a pen and some ink, and was scribbling Jem's tellings down furiously as he dictated them. He managed to get through 'Will stayed behind to...' before Henry burst in and cut him off.

"A sensor!" Henry cried jubilantly, and thrust a large black box into Charlotte's hand. "Look!"

Obligingly, Charlotte took the object carefully, putting down her pen.

"Marvellous, Henry." Charlotte smiled fondly. "What does it do?"

"It can tell you when demons are nearby. Obviously it won't work here as it's hallowed ground and there aren't any demons, but switch it on, Lottie."

He reached an oil-stained hand over and pressed a button on the side, leaving a streak of black on Charlotte's pale hand, which she delicately ignored. She laid it on the table and they all watched.

"It's surveying." Henry explained. "Checking for demons, then it will ping because it is a safe..."

Just then, punctuating the air with an ear-splitting volume and cutting over Henry, was a wailing so loud all of them threw their hands over their ears. Moments later, Jessamine flew into the room, her hands too covering her ears to avoid them shattering.

"What is that sound?" she screeched. "It is horrible!"

"I...that's the sound it's meant to make when there are demons present." Henry yelled, deflated.

"I think it needs some work, dear." Charlotte shouted, her voice somehow remaining even.

By the time the noise had died down, much to everyone's relief, Jem's ears rung. In the commotion, Ciel and Sebastian had left the room unnoticed.

"I suppose it was too loud." Jem said, trying not to laugh.

"And who could blame them?" Jessamine huffed, and flounced from the room.

If only Will was here, Jem thought, grinning. He would be devastated he had missed this. Henry, meanwhile, was at a loss. He was so sure this prototype would work. He tested it with demon blood, and it had worked. It had never activated unprovoked before. Oh well, he thought with a sigh as he retreated to his laboratory. Back to the drawing board.