When Jim's mother's memories of the Troll world reemerge, she gathers Tobia and Claire's parents together to confront their children about their activities as the kids struggle to invent a cover story.
A long-dormant ally shows Jim and his friends what really happened at the Battle of Killahead. Gunmar awakens Morgana, and Angor Rot plots his revenge.
Even while the Trollhunters gather components for Merlin for a spell, Jim's only chance to avoid being held back at school is to show around a pair of new and very strange exchange students.
As Gunmar hunts for the key to free Morgana, Merlin ruthlessly manipulates Jim into making a dramatic and irrevocable choice for what he considers the greater good.