With the help of an ancient troll-hunting tool, Jim and Toby try to unmask the changelings living among them; Claire presents Jim with a tempting offer.
A fifteen-year-old boy stumbles upon a magical amulet that transforms him into a warrior with the title of Trollhunter. He is the chosen defender of the trolls that live below the human town of Arcadia from miscreants who try to disrupt peace.