It's 1935 and twelve-year-old Moose Flanagan and his family have just moved to Alcatraz, the island that's home to criminals like Roy Gardner, Machine Gun Kelly, and Al Capone. Kids living here—because their parents work in the prison—are all cowed by danger-loving daughter of the warden, Piper Williams. Now Moose has to try to fit in at his new school, avoid getting caught up in one of Piper's schemes, and protect his sister, Natalie, who's not like other kids.