When Lydia goes missing from the hospital, werewolves and hunters begin a search.

Isaac's father is murdered; Scott, Stiles and Derek plan a break-out. At the same time, the Argent family remove the principal and Allison's grandfather replaces him. Scott senses that another werewolf is in the lacrosse locker room and plans to sniff them out, literally.

Scott tries to keep Derek from creating new werewolves; Argent officially begins Allison's training; the new creature in town takes another victim.

When the new shapeshifter strikes again, Scott has to recruit a reluctant Allison to acquire a rare book in Gerard's collection, while also once again surviving dinner with her family.

Derek becomes convinced that Lydia is the shapeshifter they're after, forcing Scott to gather his friends -- and even some enemies -- to protect her.

As Lydia begins to make connections about the bite from Peter, Jackson causes new problems for Scott and Stiles while Derek has a crisis of faith in his leadership as a new Alpha.

During a secret concert, Scott and Stiles come up with a method to trap the new shapeshifter. At the same time, Allison's mother comes up with a plan of her own to take care of Scott once and for all.

Even as his relationship with Allison becomes further strained, Scott and Stiles must attend Lydia's birthday party while Derek locks his new wolves up to watch after them on their first full moon together.

Scott, Stiles, Melissa and Stillinski are taken hostage; Allison tracks Derek to the station.