Al Capone Does My Shirts is a novel by award-winning author Gennifer Choldenko. In this novel, Moose Flanagan and his family move to Alcatraz Island, where Moose's father has gotten a job as both electrician and prison guard for the federal prison situated on the island. Moose misses his friends back home and resents his mother for uprooting the family for another of her schemes to help his sister Natalie be normal. Almost immediately, Moose finds himself in trouble when the daughter of the warden, Piper, draws him into a scheme to make money off of the name of the most famous prisoner at Alcatraz, Al Capone. However, Moose soon learns he does not need Piper to find trouble. Al Capone Does My Shirts is a humorous novel that can also bring a tear to the reader's eye as Moose learns that family is worth fighting for.

Moose Flanagan is unhappy with the move to Alcatraz because he misses his friends and grandmother back in Santa Monica. To make matters worse, Moose's father is working so much that he does not have time to toss the ball with Moose. However, his father does have time to take Natalie for a walk to give his mother a break. It is all because of Natalie they are there in the first place, so she can attend the Esther P. Marinoff School in San Francisco.

Theresa Mattaman comes by the apartment their first morning there and takes Moose and Natalie on a short tour of the island. They run into Piper, the warden's daughter, who immediately asks uncomfortable questions about Natalie. Moose does not like it when people assume Natalie is stupid simply because she is different. Piper's questions just make Moose dislike her.

The next morning, Moose and his family take Natalie to her new school. Natalie is aware something is happening and nearly refuses to get off the boat, but Moose manages to convince her to go. Back on Alcatraz, Moose thinks about all the other attempts his mother has made to fix Natalie, including a study at UCLA that ended with the doctors telling his mother there was nothing they could do for Natalie. Moose thinks it was then when his mother insisted that Natalie was only ten, each and every birthday since.

The first day of school in San Francisco is exciting for Moose, who discovers a group of boys who organize a baseball game every Monday. Moose is riding high as he makes his way home, but his bubble burst when he receives a phone call from the Esther P. Marinoff School asking his parents to come pick up Natalie immediately. Moose goes with his mother to the school where they are told that Natalie is simply not ready for their program. The dean of the school gives Moose's mother the name of a woman he claims will help, another dead end road as far as Moose is concerned.

Piper comes up with a scheme to have kids at school pay to have their clothing washed in the prison laundry for a nickel each. Piper wants Moose's help, but he repeatedly refuses, afraid of compromising his father's job after the warnings the warden gave him. Piper persists, however, eventually getting caught and causing not only Moose, but Annie, Jimmy, and Theresa to get in trouble as well.

As part of Natalie's new therapy, Moose is required to keep her with him during the afternoons, even when he goes out to play ball. Moose decides to search for a ball hit over the wall by the prisoners to give to his new school friend, Scout. Moose leaves Natalie to count rocks or buttons as he searches. One day, Moose discovers that a prisoner working as a gardener in the area has befriended his sister. Moose becomes frightened that this criminal has done something unspeakable to his sister and refuses to take Natalie out of the apartment again. However, Natalie is able to communicate to her her desire to see her friend again. This time, Moose allows it as long as he can see what is happening.

It has become clear to Moose that Natalie has made progress with her new therapist. Moose can also see how important it is to his mother that Natalie gets into the school. When Natalie is turned down once again, Moose goes to the warden to ask for help. When the warden refuses, Moose sneaks a letter into the prison to Al Capone. A short time later, Moose learns that the Esther P. Marinoff School has created a new program for older children and Natalie is to be their first student.