Wolf's Bane by Kelley Armstrong
Summer camp is a traditional teenage rite of passage, but when you add supernatural powers to the typically high dosage of adolescent hormones – you get an even more combustible mix. Sixteen-year-old werewolf twins Kate and Logan Danvers are none too thrilled at being shipped off to a supernatural youth leadership conference in West Virginia.
From the moment they arrive at the camp, the twins sense something is off and they react in their usual manner – Logan reserving judgement and surveying the setup, while Kate charges forward determined to get answers. Kate and Logan quickly ascertain that most of the conference attendees have already formed hostile factions, leaving the twins and a few other misfits to band together.
What seems like teen hormones in overdrive becomes something much more dangerous, even deadly. Add in a strange magic-warded cabin in the woods and a local history rife with curses and macabre legends, and it becomes clear this was a really, really bad place to build a camp for teenage supernaturals.