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