Scott races to uncover Gerard's master plan following a shocking death on the lacrosse field. Meanwhile, Derek plots to take Gerard down using his own methods.

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

Allison tracks Derek to the sheriff's station, where Scott, Stiles, Melissa and Sheriff Stilinski are being held hostage.

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.

Chris, Scott and Stiles struggle with how to stop the Kanima; Scott and Stiles plan to trap the Kanima at a warehouse party, where Erica will also be present, while Allison's mother plans to take Scott down. Chris and his team of hunters face Derek in a confrontation.

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.

Derek believes that Lydia is the shapeshifter they are after; Scott gathers forces for protection.

Derek believes that Lydia is the shapeshifter they are after; Scott gathers forces for protection.

The new shape-shifter strikes again, and Scott recruits a reluctant Allison to acquire a rare book in Gerard's collection.

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

The night before the new full moon, Isaac's father is murdered. When he's taken into custody, Scott, Stiles and Derek resolve to break him out before the Argents get to him first and before the newly bitten teen turns into a werewolf.

When Lydia goes missing from the hospital, werewolves and hunters alike begin a search to discover not only where she is, but what she's become.