Will turned, watching Sebastian retreat back down the corridor. Then he looked back at the door, took a breath, raised his fist and rapped sharply on the wood. Catarina opened the door and beckoned behind her. She moved back to Jem's side, and Magnus took her place in the doorway.

"Is he alright? May I see him?" he asked, voice tight.

Magnus reached a hand out and laid it on Will's arm, both to comfort and to pull him gently into the room. The warlock got the feeling that, without his catalysing, Will would stay frozen on the threshold forever. Will walked slowly over to Jem's bed and got gingerly to his knees, taking his parabatai's hand.

"He looks exactly the same." He said, concerned.

"Feel his heart." Catarina said quietly.

Will moved his hand up to Jem's wrist, where a steady, rhythmic thumping thrummed under the thin, papery skin. "You stabilised his heart." Will said, vacant but relieved. Then he pulled back, worried. "But why did you call me if he was alright? What's wrong with him?"

"Nothing, he is alright, Will." Magnus assured him consolingly. "But the two of us, and Ragnor back in London, have been researching methods to try and cure Jem. And we have found...a couple of things."

Will sat down on the edge of the bed, blue eyes wide. He opened his mouth to reply, but he couldn't sculpt any words. Instead, his eyes went to Magnus, silently asking him to explain.

"We have two options." Catarina said, bending down beside Jem's bed on the opposite side to Will. She placed a damp cloth on his forehead and patted it against the skin softly. "Our first option is to burn out the demon poison with heavenly fire."

"Which we don't have a ready supply of." Magnus added.

"What is the second option?" Will asked quietly.

"Another thing we do not currently have a supply of – but is slightly easier to obtain." Magnus said.

"Demon blood." Catarina finished.

"What?" Will gasped, involuntarily clutching Jem's hand. He loosened his grip at once, casting Jem an apologetic look the other boy could neither see nor return.

"Yin Fen – the drug making Jem so unwell, but keeping Jem alive for the moment, though perhaps not for long – some research Ragnor has unearthed suggests demon blood may reverse the effects. Demon does not affect those with demon blood – which is why demons cannot kill other demons, and their blood is potent, so it will take effect with very little in Jem's body."

"That seems counter intuitive." Will said weakly. "You want to inject him with demon blood to reverse the effects of demon poison?"

"In short, yes." Magnus said.

Catarina handed the cloth she had been wiping Jem's brow with over to Will and stood up.

"We received this fire message from Ragnor, detailing all the information he found on the cure." Catarina explained, washing her hands in a water basin and picking up the letter in question, drying her hands on her skirts. "Whilst he does say all the evidence points to the fact this method clearly works – and has been executed more times than the heavenly fire method – it is not without risk."

"Just tell me." Will said, resigned. "I cannot be any more concerned than I already am. Tell me."

"As we do not have very many accounts of this cure, the effects are questionable, but we do have a few...ideas as to what the after effects this method might be accompanied by." Magnus explained.

"Which are?" Will prompted.

"The equivalent to this we can find is the procedure to create Forsaken warriors." Catarina said. "Our concern is that, depending on how potent the demon blood we give Jem, the angelic and the demonic will war within him. And we are...uncertain if it will be survivable. And, as Jem cannot consent to the treatment, we need someone to authorise it." Catarina nodded. "That would be you, Will."

"What about Charlotte? His...guardian? His real family?"

"I think Jem would probably agree that would be you." Magnus said gently.

"May I...I will think on it. I...need a moment. Some air." Will said, stumbling gracelessly as he stood.

"Not to pressure you, but it would be wise to decide as soon as possible." Catarina said, and the shadowhunter understood the implications behind her words: time was running out.

Will raced down the mansion's hall, dripping and diving around corners. He had sprinted straight past Ciel's office, not entirely sure where he was headed. He wasn't even sure why he was running; his lungs – air tearing in and out of them and burning like fire – were screaming at him to slow down. But his heart was beating so hard, he felt so out of breath – he wanted to at least give his body a reason to feel like that. If he stayed still, he thought the nervous energy might kill him. He flung open the manor's backdoors, taking the stone steps into the garden two at a time. He looked up suddenly, sensing a presence, and saw Sebastian, bent to the floor on one knee, a bundle of white in his arms.

"Sebastian," Will said, raising his voice to be heard. "May I talk to you?"

The white bundle mewled and Sebastian placed down the small stray cat, who bounded off into the hedgerow. The act comforted the shadowhunter somehow. He thought back over the past few weeks, images of the butler sliding in his mind. Finding the captured Ciel, releasing them from the Seelie Court, killing guards and vampires, silently comprehending information and formulating plans and escapes. Sebastian was competent – never phased. Will sat down on a bench hidden in a hedge-walled alcove. Sebastian stopped before him, ever obliging.

"I would appreciate some assistance. I have a problem." Will told him.

"It would be my honour to be of service." Sebastian replied, compliant.

"Jem has been ill for a long while now with a drug that a demon made him addicted to." Will said, looking up to see Sebastian's response, which appeared to be one of sympathetic passivity. "He was told he may not last the year out – and that was three years ago. However, now, it looks as if that may be correct. This time, I fear he truly will not recover."

"What makes you fear that?" Sebastian enquired.

"He hasn't woken since he fainted." Will explained. "I can tell. It feels different to when he's been unwell before. I know."

"The two of you are very close." The butler observed.

"There's probably more of me in Jem's heart than in my own soul."

"Does Jem feel this too? He knows the ins and outs of your very heart?"

"Of course." Will answered.

"Then you have your answer." Sebastian replied. "Have you not? You know Jem better than anyone – perhaps even better than he knows himself. You know what Jem would have you decide."

"Jem is brave." Will said quietly. "He is a fighter. If there was any way to keep him alive, he would want me to do so." Will looked up. "Thank you, Sebastian."

"If I could not offer my master's friend some prudent advice, what sort of butler would I be?" Sebastian told him. "Will that be all, Mr Herondale?"

"Yes. W-wait, please could you go and tell Magnus and Catarina I want them to do anything they can to help Jem. And if there's anything they need, could you try and get it for them? Oh, and let Magnus know I'll be up in a moment, and not to do anything risky until I arrive." Will paused, smiling a little. "Sorry, that was rather a lot of instructions."

"I'm sure I shall manage." Sebastian replied, smiling politely.

Will reached a hand out and caught at Sebastian's sleeve as he turned to go. The butler spun back to face Will, ready to comply with whatever the boy asked of him.

"Thank you."

Sebastian blinked, surprised, before regaining his calm façade.

"It is my pleasure, master Herondale." He replied, and Will watched him go.