Jigsaw Jones and Mila go undercover to find out who has stolen Ralphie Jordan's old bicycle, but the big challenge is figuring out who would want a hand-me-down bike.

As the class prepares for the holidays, Jigsaw takes the case of Lucy, who has lost her father's rare coin, and the mystery means having to interview a big, tough second grader named Bigs Malone.

Jigsaw faces off against Reginald Pinkerton Armitage III, a rival detective who, unlike Jigsaw, uses fancy gadgets and personal charm to solve mysteries.