Moose Flanagan, who lives on Alcatraz along with his family and the families of the other prison guards, faces new challenges when his father is promoted to Associate Warden. The Flanagan's apartment catches fire and Moose and his friends need to find out who started the fire.

Moose has his hands full during the summer of 1936 watching his autistic sister, Natalie, and the warden's daughter, Piper, and trying to get on a baseball team by proving he knows Al Capone.