The Pack mourns Pete, but their quasi-funeral is interrupted when they catch scent of a mutt outside. Racing into the woods, they find Pete's jacket hanging from a tree. So this killer mutt is subtle, obviously. Clay suggests to a stressed Elena that they go for a run to calm down. The two wolves frolic and roll around and flirt AS WOLVES (it's possible) before transforming back to (naked) humans and passing out in the dirt. Clay wakes up first and plants a kiss on Elena, who responds and then quickly pushes away. She later tells him that was a mistake.
Meanwhile, we see the aforementioned killer mutt transform back to human. He's a bald dude with glasses and he's got a look of intense creepiness as he walks down the street.
Philip calls Elena, who misses him and feels terrible for lying to him (about being a dog - literally - amongst other things). She promises to be back in Toronto for his sister's wedding.
Jeremy talks with the sheriff, who tells him the body of the little boy discovered in Episode #3 was dumped on Jeremy's property; it is clear the child was killed elsewhere. The sheriff's suspicions are peaked. Jeremy tells Tonio he blames himself for Pete's job. His role as Pack master is to keep everyone safe and he failed. Jeremy tells Tonio to chat with the other Packs. If others are being targeted, there's a larger issue going on. If it's just their Pack, Jeremy will know it has something to do with him.
Nick goes to find information on the killer mutt that murdered people at the rave in Episode #3, while Elena and Clay see if they can get a trace of the mutt that killed Pete. She gets a scent, which leads the two ex-lovers to a motel. They break into the killer mutt's room and find a scrapbook detailing murders of women across the country - except these aren't wolf kills. These were kills made by a human. They surmise that the killer mutt was a psychopath who was purposefully transformed into a werewolf. Outside the motel, they spy Zachary Cain - a noted mutt and enemy of the Pack - conversing with the killer mutt in human form (the bald dude with glasses from earlier in the episode). A car pulls up and Karl Marsten, the british guy that offered to help the Pack last episode, steps out. He's in cahoots with the Pack's enemies. Elena and Clay grab the scrapbook and bolt.
Back at Stately Wayne Manor (a.k.a. Stonehaven), Elena and Clay share their findings with Jeremy and Nick. Nick reveals that he learned the killer mutt shot at the rave last episode was named Scott Brandon and was an ex-con. The Pack theorizes that Karl, Zachary and potentially others are purposefully turning psychopaths into werewolves to send them after the Pack. Jeremy's theory is that they want to destablize or wipe out the Pack. In doing so, there would be no one around to keep order amongst mutts. They's run wild, their presence would be revealed to humans and all-out war would erupt. So, Karl, Zachary and whoever else are either a) anarchists or b) think they could win the war.
Back in Toronto, Logan gets a visit from Daniel Santos, a former Pack member who apparently split on bad terms. Oh, and Clay killed his brother. Anyway, Daniel offers information on the killer mutt(s) in exchange for being welcomed back to the Pack. Logan offers to bring him to Jeremy.
Elena, Clay, Nick and Jeremy head back to the motel to confront the killer mutt. The place is boobytrapped with a loaded shotgun (Clay is nearly killed). Inside, they find Pete's finger and a warning to Elena scribbed on the wall: "I'm coming for my scrapbook, bitch."