It's 1935 and twelve-year-old Moose Flanagan and his family have just moved to Alcatraz, the infamous island that's home to criminals like Roy Gardner, Machine Gun Kelly, and, of course, Al Capone. Kids living in Alcatraz—because their parents work in the prison—are all cowed by the clever, 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 countless schemes, and keep an eye on his sister, Natalie, who's not like other kids. All Moose wants to do is protect Natalie, live up to his parents' expectations, and stay out of trouble. But on Alcatraz, trouble is never far away.