When they cross the boundary into Hale territory, Stiles shifts a little in his sleep, shoulders hunching. Lydia's immunity carries over into most of the supernatural world: she can't be bitten, she can't be poisoned, and she's never been able to do magic on her own. Unlike Stiles, she can't feel the veil that separates Beacon Hills from the rest of the world. Sometimes she wonders if what happened before they left would have turned out differently if she'd undergone some transformative alchemy, but usually she tries not to think about it at all.

Six months after Derek and Cora leave Beacon Hills, Stiles gets a text from Cora – they’re in trouble and need help. Turns out that Derek is being wooed by a neighboring pack. The Alpha remembers his mother fondly and would love to have a Hale in her pack. Especially if that means she might breed in the ability to change into a full wolf. And she’s not taking ‘no’ for an answer, even when Derek lies and tells her that he already has a mate. Except Derek didn’t lie. When Stiles shows up to help with the emergency, he inadvertently discovers that he is Derek’s mate. Stiles tries not to think about it (he knows that the mate bond isn’t written in stone, just look at Scott and Allison) as he (and Lydia, and Deaton) research mates and the challenges to the mate bond (because, of course there’s a ritual for that) and try to keep the Alpha of the Palmer pack from discovering Stiles’ connection to Derek. Throw in the monkey wrench of Peter showing up, and Stiles starting to have feelings, and Derek sometimes looking at him like . . . Stiles doesn’t know, but he doesn’t hate it, and things begin to get a little bit complicated.