The Sinister-Winterbottoms, twins Alexander and Theo and their older sister Wil, find themselves at a mysterious summer camp where they meet other families whose parents are missing.
Following the clues left behind, Theo and Alexander find themselves at Siren's Song Seaside Amusement Park, where they must work together to escape, stop their newfound nemesis Essa, save Wil and their friends, and find their parents.
Aunt Saffronia drops the Sinister-Winterbottoms off at the Sanguine Spa, which is possibly owned by vampires, and where they must continue to complete the tasks they have been set if they are to see their parents again.
Twins Theo and Alexander and their sister Wil are abruptly dropped off at their Aunt Saffronia's house, where they learn they must complete a series of tasks in order to see their parents again--and their first assignment is at a waterpark.
