When Claire Cooper was eight years old her mother mysteriously vanished during Hop-tu-naa, Halloween on the Isle of Man. At fourteen, Claire is still struggling to come to terms with her disappearance when she's befriended by a group of five teenagers who mark every Halloween by performing dares. But Claire's arrival begins to alter the group's dynamic until one year a prank goes terribly wrong, changing all their futures and tearing the friends apart. Six years later, one of the friends is killed on Halloween in an apparent accident. But Claire, now a police officer, has her doubts. Is a single footprint found near the body a deliberate taunt? As another Halloween dawns, bringing with it another death and another footprint, Claire becomes convinced that somebody is seeking vengeance.