Moose Flanagan and his family move to Alcatraz—a tiny island off the coast of San Francisco that houses some of the country's most dangerous criminals. Moose is less than thrilled about being away from home, stuck on a cement rock where most of the population is behind bars. Which seems like a totally legit reaction to this development.
He's also less than thrilled about having to keep an eye on his autistic sister, Natalie. Natalie was accepted into the Esther P. Marinoff School, which was supposed to help her, but unfortunately, she's sent back home almost immediately because she's just not adjusting to the school. Which means that Moose becomes her caretaker. The question is: What does one do with an older sister who needs constant supervision on an island infested with dangerous criminals?
Moose makes friends with other kids on the island, including Piper, the warden's daughter. Piper devises all sorts of crazy schemes to keep them occupied, most of which involve breaking Rule Number 1: Don't talk to or about the prisoners.
Most of these schemes turn out to be flops. Case in point: Piper starts a criminal laundry service for the kids at school, but the kids lose interest really fast. Moose starts hunting around outside the prison's rec center every day, though, hoping to find a stray baseball. Kid's got to keep himself amused somehow, after all.
His search is a total failure, though, until he finds out Natalie's been making friends with one of the cons. And this con has been hanging around long enough to know what Moose is looking for, so he gives the kid a ball. Suddenly, though, it doesn't seem like such a prized possession to Moose.
He is super scared for his sister, and his exploring quickly comes to an end. This kind of backfires, though, since it turns out that being out and about has helped Natalie adapt to the world around her. Out of ideas for how to help her, Moose's family applies to the Esther P. Marinoff School again, but are rejected.
In his riskiest move to date, Moose decides to take matters into his own hands and writes a letter to Al Capone—the infamous gangster at Alcatraz—asking him to use his connections to help his sister get into school. And guess what? Within days, Natalie is accepted into the Esther P. Marinoff School. Huh.
Was Capone a part of this? Well, let's just say that Moose finds a rather cryptic note in one of his convict-washed shirts… right after the good news.