On the eve of the start of senior year, Scott and his pack are challenged by the arrival of a new enemy.

Lydia helps a student with nightmares, while Stiles is wary of a new classmate.

Scott tracks a dangerous shapeshifter that has been threatening Stilinski.

Stiles works on tracking down a fugitive; Liam tries to be Mason's wingman at a nightclub.

The pack enters Eichen House in order to learn more about the Dread Doctors.

Scott and his friends follow Dr. Valack's advice and experience strange effects as a result.

Scott tries to trap one of the doctors. Meanwhile Stiles and Theo try to figure out who is taking the dead bodies.

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.

While Scott turns to an unlikely ally for help, Stiles and Lydia try to uncover the truth about Parrish.

With both lives and friendships on the verge of being destroyed, Scott and his pack face their greatest enemy yet.

Scott, Malia, & Stiles scramble to find a way to save Sheriff Stilinski from an unknown toxin while Liam & Mason search for the whereabouts of Hayden's body and the other dead chimera bodies.

Without the support of his pack, Scott considers that the Dread Doctor's success could mean for Beacon Hills.

Kira's mother sets out on a journey with Kira to help her maintain control of her dark side; Lydia receives a surprise at Eichen House.

As Scott tries to put his pack back together, Malia and her new ally set out to rescue Deaton from The Desert Wolf.

After finding out that Lydia is in danger, Stiles makes a plan to break her out of Eichen House; Theo has his own plans as he joins Deucalion in a quest to kill Scott.

While trapped in Eichen House with Theo and the Chimera pack, Scott tries to rescue Lydia before time runs out.

Scott and the pack try to use a charity lacrosse game to figure out the identity of the Beast.

Now that the beast's identity is known, Scott and his pack race against time to stop the Dread Doctors.

Loyalties are tested and new alliances forged as Scott and his friends work to stop the Beast before Beacon Hills is razed to the ground.