Deaton finds him a few hours later, hunched in on himself in the back room of the man's clinic. He takes one look at Derek and sighs. "I take it things didn't go as planned?"
Derek doesn't want to tell him. He doesn't want to have to tell anyone anything, wants none of this to have happened, wants his pack to be whole and safe and loyal, but apparently he's getting none of that today. What's one more thing not going his way, in the grand scheme of things? "The kanima's master took them hostage before I could get there. The Argents showed up, and..." He swallows around the lump that's been rising in his throat since he heard that first panicked whisper. "Scott's working for Gerard."
His eyes squeeze shut. Blurting it out hasn't made the betrayal hurt any less, but the flat, almost unsurprised way Deaton reacted makes him feel all the more stupid about it. "How is he the one I need trusting me," he snaps, "if he's working with them?"
"Maybe if you'd trusted him sooner, he wouldn't have thought he had no other option," Deaton suggests mildly. Derek buries his head in his hands, reminding himself that for some reason his family - his mother - had trusted this man. Killing him now would be spitting on their memory. He still entertains the idea, but only as a distraction from every other awful thought trying to make itself known. When Deaton adds, "I've seen Gerard take advantage of people like that before," it hits like a blow to the head, knocking all his thoughts out of place, only for them to reassemble into a blinking neon sign that reads 'ALL YOUR FAULT'.
He grits out, "Well, there's nothing I can do about that now, is there."
"Not necessarily. If I know Scott, he's kept his involvement with Gerard a secret. He's a lot like you that way - thinks keeping the truth from people protects them." Derek doesn't rise to the bait, but only just. "Which means... you still have an in with him, if you can use it properly."
It takes Derek a minute to realize what he means. His eyebrows shoot up involuntarily. "Stiles?"
"Scott trusts him," Deaton says simply. "Stilinski may not trust you, but he's pragmatic. If he decides you're the lesser of two evils, he can convince Scott to work with you. It won't be the familial bond you've been hoping for, but at least he won't be working against you."
Derek sighs. He hates this. He knows he's not thinking clearly - half of him wants to lash out, make Scott feel as torn down and broken as he does, and the other half wants to wallow in guilt and self-recrimination - but Deaton's right. He's got bigger problems. And though he hates to say it, the man's suggestion makes sense. Except for one thing. "And how am I supposed to convince him of that?"
"Try the truth. You'd be surprised how well people respond to it."