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.

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.

Scott plays in the championship lacrosse game and must figure out a way to stop Gerard. Meanwhile, Allison continues her hunt for Derek and his pack.

Scott races to uncover Gerard's master plan following a shocking death on the lacrosse field. Derek plots to take Gerard down using his own methods. Erica and Boyd are captured as Allison continues her merciless bloodthirsty revenge on the werewolves for her mother's suicide. Meanwhile, Scott, Stiles, Lydia, Melissa and Isaac are all under pressure amidst the chaotic events.

Allison and Lydia locate a possible clue to finding Boyd and Erica while one of Stiles' childhood friends goes missing.

While Scott tries to keep Isaac from engaging in a deadly confrontation with the Twins in school, Stiles attempts to prove his theory that the killings have nothing to do with werewolves.

During a bus ride to a cross country meet, Scott and his friends flash back to the events of a preemptive strike against the Alphas that has left several injured and possibly one or more dead.

As the danger begins to reach closer to Scott, threatening his trusted mentor and boss, Deaton, Kali and the Twins go after Derek.

As Allison begins to suspect someone dangerously close to her may be involved in the murders, Scott and Stiles conclude that Lydia’s rising talents may be their best bet to solving the murders.

With the threat growing far more personal and time running out on innocent lives, Scott is forced to make a difficult choice in order to save both friends and family while, at the same time, Derek and Peter try to figure out how to save Cora’s life.

Scott and the others seek an important artifact; Stiles must make a decision about Eichen House.

Scott and Malia get help to try to find Hayden and Liam. Deaton discovers something horrific about the dread doctors. Hayden and Liam will be faced with a life and death situation.