Moose Flanagan lives on a famous island in California: Alcatraz, home to some of the most dangerous prisoners in the United States in the 1930s. It s the summer before he starts high school, and Moose is going to play a lot of baseball and win a spot on the high school team. But he still needs to watch his special older sister, Natalie and then the warden asks Moose to look after his two-faced, danger-loving daughter, Piper.