School has just started and Korina has already taken a dislike to her new lab partner, Riley Gadwalder, a loudmouth who chews bubble gum. But she has bigger things on her mind: the Puzzle Club is baffled by a series of pet disappearances throughout the city of New Bristol. When Korina finds a gum wrapper in the grass, she suspects Riley of the pet-nappings, but then Riley disappears, too.