Derek is on the hunt for a killer while Lydia gets some uninvited guests at the lake house. 

Sheriff Stilinski wants everyone off the roof where Sean was killed while he has his own expert come in to examine the scene. Parrish is skeptical, but he does it and Derek assists.

Scott has Liam duct taped in his bathtub. He calls Stiles for an assist.

Liam feigns tears and then attacks the boys when he's set free. He runs of into the night.

The muted one tosses a pick ax into Peter's chest, punches something into his wrist band and announces Derek is next.

Stiles is trying out restraints on Malia when Stilinski walks in. It's not what it looks like.

Lydia and Kira take a look at the code in Lydia's math notes. Lydia's mom pops in with the keys for the lake house.

Liam runs to school. Scott and Stiles catch up with him. Scott tries to tell Liam they're brothers now and the bite is a gift. Stiles begs him to stop. Liam refuses to believe anything is happening to him. He pulls off his bandage and is healed -- proof!

Lydia suggests the trickster use her foxy powers to be a vixen to attract Liam to to the lake house. She slinks her way down the steps and falls half the way. 

The ax was laced with some kind of wolfsbane and Derek has to burn it out of Peter with a torch.

Scott discovers his "little brother" has some serious anger issues.

Liam freaks out after seeing Malia and his senses are uber sensitive. He invited his friend Mason and the gang's all at Lydia's.

Derek takes the voice device to Stilinksi. They discover the muted one has been paid -- he's an assassin. 

Kira knocks out Liam and Stiles tries to restrain Malia in the basement.

Damn. Some bitch stumbles upon a wolf who can keep himself from transforming using a mantra and she beheads him. Not cool. She captures a photo. For posterity? No. Her boyfriend gets a text -- money has been transferred to his account. Totally not cool that he had her do the dirty work. Loser.

Lydia cannot hear anything but background noise when the door to the party is open. There is a vintage record player in the room, and she turns it on. She hears voices and faces start to pop out of the walls, attempting to speak.

Scott and Kira slow dance and kiss out by the lake. She hears growling. It's Liam. He breaks his chains and escapes.

Stiles is dealing with Malia, thrashing about. He tries to calm her with his voice without results.

Stilinski and Derek go to the high school after dark.

Stiles tells Malia control is overrated and releases her. After she stops thrashing, she can control her turn.

Liam attacks Scott and screams that it's all his fault. Someone tranqs Liam. It's Argent!

When Stilinski arrests the mute, Peter jumps him, pummels him and rips out whatever type of heart he may have. Stilinski wants to shoot Peter, but Peter just shakes his head at the sheriff and walk away.

Liam finally asks what's happening to him.

Kira finds Lydia in the room listening to the end of a record play down. She hears the key to break the code.

Liam is worried his mom and step-dad will know about this, and he doesn't want to do it to them again. He doesn't want them to see him angry again. Like a monster.

Lydia has the dead pool. The key was "Allison."