When Lydia suffering from hallucinations goes missing from the hospital, werewolves and hunters alike begin a search to discover not only where she is, but what she may have become.
The night before the new full moon, Isaac's father is murdered by a strange creature.
Scott struggles to stop Derek from creating new werewolves, while Chris Argent decides to officially begin Allison's training as a hunter.
When the new shapeshifter strikes again nearly claiming Stiles and Derek Scott has to recruit a reluctant Allison to acquire a rare book from Gerard's collection, while also once again surviving dinner with the Argents.
Derek becomes convinced that Lydia is the shapeshifter they're after since she seemed immune to its toxin, forcing Scott to gather his friends and even some enemies to protect her from the Alpha.
With startling new information about the shapeshifter, Scott and Stiles hurry to protect their friends while Allison is given an investigative task by her family.
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 abilities as a new Alpha.
During a secret concert, Scott and Stiles come up with a method to trap the new shapeshifter.
Stiles comes to a major realization about the murder in Beacon Hills and a possible connection to Isaac.
With a shocking secret revealed, Scott, Stiles, Melissa and Stilinski are taken hostage in the Sheriff's Station.
Scott must help win the championship lacrosse game while also trying to figure out how to stop Gerard.
Even though everyone is still reeling from a shocking death on the lacrosse field, Scott and his friends rush to figure out Gerard's master plan while Derek plots to take him down using his own methods.