David Vandergraff lost his home, his job, and contact with his oldest son, but remains determined to be a good husband and father despite being a dark winter wizard. His resolve is tested when a flyer for a missing girl—who happens to be a summer witch—begins to haunt him. David believes a spell needs to use him to save her, so he follows the magic's command and looks into her disappearance. His teenage daughter Emmy resents him for caring so much about a random stranger. But when she uncovers some disturbing evidence close to home, she begins an investigation of her own. David and Emmy quickly learn that the mystery is not only about a missing girl they barely know, but a deeply personal story that impacts everyone they care about. As their world crumbles, they fear the warning may be true—never mess with summer wizards, because the good guys always win.