The Mysterious Monsters hiding in the Mattigan's basement have
discovered they have something in common. When clues about this link
point to an island in Canada, one where a werewolf has recently been
sighted, Maddie, Max, and Theo convince their dad it's time for one more
mission. The kids are determined to help their friends uncover the truth
about their pasts--but also to uncover the truth about their own.