Realizing the success they're having in detective class, Cubby Roo, his master and three of their friends form their own mystery detective club. While Cubby and Harry take a walk in the woods the next day they encounter a man dying of multiple stab wounds.
Unhappy about these sleuths being at the crime scene upon his return the killer comes after them. Cubby and Harry aren't the only ones worrying about staying safe, as their partners must hide when burglars return to the house they previously burgled items from.
In another case, tourists are frightened out of a haunted museum. The detectives must flee for their safety too while trying to solve the mystery.