Alcatraz Island in the 1930s isn't the most normal place to grow up, but it's home for Moose Flanagan, his autistic sister, Natalie, and all the families of the guards. When Moose's dad gets promoted to Associate Warden, despite being an unlikely candidate, it's a big deal. But the cons have a point system for targeting prison employees, and his dad is now in serious danger. After a fire starts in the Flanagan's apartment, Natalie is blamed, and Moose bands with the other kids to track down the possible arsonist. Then Moose gets a cryptic note from the notorious Al Capone himself. Is Capone trying to protect Moose's dad too? If Moose can't figure out what Capone's note means, it may be too late.