Turtle is an eleven-year-old girl who is being forced to move from New Jersey to Key West due to her mother’s work. The only catch is that she is moving without her mother to live with her Aunt Minerva ("Aunt Minnie"). She heads on a road trip with Mr. Edgit, who is doing a favor for her mother's lover, Archie, down to Key West. On the way there Turtle thinks about all of the rotten things kids have done to her, such as get her mother fired with lies or set her cat Smokey’s tail on fire. Turtle doesn’t fare much better when she arrives in Key West. Finding Curry Lane where her Aunt Minnie lives Turtle meets her cousins Beans, Kermit, and Buddy. While Kermit and Buddy get along well enough with her Beans does not. Kermit is perhaps the most welcoming, and it’s found out that he has a weak heart because of having Rheumatic fever when he was younger.

Aunt Minnie ends up throwing the four out of the house when they get to be too much and Turtle learns that they, along with their friend Ira, are running a babysitting business for candy called the Diaper Gang. They pull around a cart with the words "Will Wurk for Candy" and have only four basic rules: No girls allowed, keep your cloth clean, always duck, and never reveal the secret diaper rash formula. The first baby they pick up is Pudding and after showing they know what they are doing Beans tells Turtle that because she is a girl she can’t join the Diaper Gang. As they go by the waterfront Turtle meets Slow Poke, who is returning from harvesting sponges. He is Turtle’s biological father but at the time Turtle is not aware of this.

The next day Turtle is invited by Kermit to go out with the Diaper gang rather than stay at the house with Buddy. The day ends with the kids sitting on the porch as the ice cream man comes along. Beans tells them that he is going to trick the ice cream man into getting her some ice cream for free but in the end fails. Turtle goes up to the ice cream man and tricks him into giving her ice cream for free. She goes back to the porch and taunts Beans about not getting ice cream and when he asks for some she lets Smokey the cat have some ice cream to get back at him for feeding the candy Kermit was going to give her to Termite the dog.

A few days later Turtle is on the porch playing with her paper dolls with Buddy when Aunt Minnie comes out. She sees the dolls and starts yelling at Turtle talking about how they are her dolls that Sadiebelle stole from her when they were children. Turtle hands the dolls to Aunt Minnie, who snatches them away from her and goes inside. Later on, the Diaper Gang is playing Klee-klee, a game of tag, when Aunt Minnie comes out yelling at Kermit for running around and stressing out his heart. As she goes inside Kermit turns to Turtle and asks if she wants to go to Duval Street before the two run the entire way there. As they get to Duval street Turtle wants to look for a job. Kermit takes her to Johnny Cakes, who is a rumrunner, who turns her down. Next, Slow Poke offers to let her work for him collecting sponges the next day. He tells her to look for his boat the Lost Love before they go back home.

The next day Turtle arrives to work with Slow Poke. He asks her if she can swim, and she lies. They board the Lost Love where she meets Ollie, the new first mate. She asks what happened to the old one and Slow Poke says that he got bitten by a shark and left. In reality he means that his first mate fell in love. Turtle starts to ask Slow Poke how well he knew her mother and he is very withdrawn about the subject. However he still asks a fair amount about Turtle’s mother. He still loves her and yet is reluctant to tell Turtle anything about it, probably because of the pain over being too late to marry her. As they get to the site for sponges they spend a good part of the day pulling them up. Slow Poke asks if Turtle would like to pull the last one up when she falls into the ocean, nearly drowning. Slow Poke pulls her up from the boat telling her that the incident took ten years off of his life.

Some time later Turtle is going around with the Diaper Gang again as they go back to Pork Chop’s house. After lunch Pork Chop’s mother sends them on an errand, to bring Nana Philly her lunch. As Turtle meets Nana Philly the woman is less than hospitable, barely saying two words to her before going back to her magazine. It’s only after they leave that Turtle learns that Nana Philly is her grandmother. Turtle remembers her mother telling her that her grandmother was dead and says that is impossible only to realize that he mother was in fact lying.

Later on while the gang is swimming down at the beach Ira arrives. He is the mastermind behind the Diaper Gang and was away in Miami because his brother needed medical attention due to an injury with firecrackers. He brings back with him a way to scare people, Tick-tocking; which is where a rock is tied to a long string and thrown over a house to the opposite side by a window, making it look like there is a ghost haunting the place. The first person they test this out on is Miss Sugarapple, Pork Chop and Beans’s old teacher who punished them for taking test answers. Successfully scaring her the Diaper Gang sets out to terrorize everyone else they had an issue with in the past. The end up doing it so much that they shirk their duties with the children, needing Turtle to help out at one point. They also start up a rumor about Key West being haunted by the weeping ghost, something Pork Chop is enraged about.

Uncle Vernon—Aunt Minnie's husband—arrives back soon. It’s noted by Turtle that with him around everyone is a little bit happier. She then starts to think about his homecoming versus Archie’s homecoming. Archie is her mother Sadiebelle’s current boyfriend who is a salesman who sells people "dreams" and encyclopedias. When he arrives home Turtle describes it as christmas as he showers the two of them with extravagant gifts. However with Vernon home there is a nice meal with everyone together. After that he and Turtle are in the living room sewing clothes back when he starts to ask her about how she likes Archie, who Sadiebelle is looking to marry. Turtle tells him that she likes him before the two get on to other topics.

Turtle takes an interest in Nana Philly as she agrees to take the old woman the lunch that Aunt Minnie has prepared. When she arrives to give Miss Bea a break Turtle serves Nana Philly her food only for the old woman to knock it to the floor. She does this over and over until Turtle starts to eat her own portion of the lunch in front of her. Three days it’s like this before Nana Philly gains a respect for Turtle and starts to eat the lunch prepared. It’s then that the two remark on their dislike of Shirley Temple as their relationship starts to improve.

August rolls around with the rain as Uncle Vernon has to return back to Matecumbe. Everyone is upset about it but Turtle is having a rough time as well. Someone stole her shoes in the middle of the night, making her think about how she got them. Her mother was trying to stretch out a pair of her old shoes for her when Archie took the pair to buy her some new shoes. She talks about how that was something a father would do and how it felt like they were a family. Her thoughts are interrupted however when Aunt Minnie is beyond upset over Smokey who has ruined Mrs. Felton’s slip. She says if it happens again then the cat goes.

A few days later Turtle bumps into Slow Poke at a bar with a few of his sailor friends.He asks how things are going and she complains about missing her shoes to him as the sailors compare Turtle to her mother. She is upset about the comparison but soon asks how well he knew her mother. Slow Poke’s friends start to choke on their drinks and before he can really answer Kermit comes running up to warn Turtle that Aunt Minnie is upset because Smokey ruined more clothing of a client. The two race back to the house to see Aunt Minnie on the porch waving the skirt around beyond furious. Later on in the day Turtle is lying on the bed with Smokey attempting to figure out what to do about the situation. The boys offer their sympathies in their own way and try to help her come up with solutions when they hear Aunt Minnie scream from downstairs. They go down to see her flailing around screaming before she races out of the house and collapses in the street, a scorpion falling out of her nightgown.

Smokey kills the scorpion as they get Aunt Minnie to see a doctor. He tells them that she needs to take it easy and Turtle and the boys help keep everything together. At one point Aunt Minnie is hallucinating thinking that Turtle is her mother Sadiebelle before dropping off to sleep again. The next time Aunt Minnie wakes up she asks about who took care of everything while she was out to which the children all inform her of what they’ve done to keep everything together. Buddy tells his mother that it was Smokey who killed the scorpion but she still says the cat has to go.

Turtle is at Nana Philly’s house sometime later and is cleaning up lunch when Smokey, who Nana Philly took in, falls into the piano. As Turtle helps her out of it she finds a cigar box containing the map to Black Caesar’s treasure. Turtle puts the things back but after some time away from the map she takes it and goes to see if she can find Slow Poke since he told her about Black Caesar originally. He’s out working with Johnny Cakes for Labor day and so Turtle takes the map to the Diaper Gang. They then decide to go and find the treasure to become rich.

The children tell their families that they are going fishing for conch as they steal Johnny Cakes’s boat and head out to search for the treasure. After a few issues the children make it onto the key and go searching around for the treasure. Just when they are about to give up around noon Turtle trips over a stone with the letter ‘C’ carved in it. The children dig up the treasure and when they return to the beach they find the boat is gone, leaving them stranded.

For a whole day the children are stranded on the island and Pork Chop and Beans get into a fight over whose fault it was that the boat was lost. In the end the children go into the shack that is on the island to stay out of the weather from by the storm coming through. It’s a horrible storm and all of the children are scared, prompting Turtle to sing a Shirley Temple song to keep them from crying any longer. The next morning the storm has passed over and a rescue team consisting of Ollie, Slow Poke, and Johnny Cakes arrives. They tell them that Too Bad and Killie the horse told them more or less where they have gone and they came to rescue them.

The children return back and are given $20,000 to split between them and Nana Philly after the money is taken out to buy Johnny Cakes a new boat. Turtle is then informed by Aunt Minnie that her mother is on her way. Turtle finds out that Archie is there too and married her mother Sadiebelle. As Slow Poke arrives he gets the news as he’s introduced to Archie and leaves, saddened to know that he’s missed out on his chance to marry her yet again. Sadiebelle tells Turtle that they are going to be moving to Georgia and will be getting the Bellewood.

It’s later on that night that Turtle is lying in bed in a hotel wondering what it’s going to be like to leave seeing as she is reluctant now to go. The next morning Archie tells the girls he has everything together and they can go and say their goodbyes. Turtle and Sadiebelle head to Nana Phillies where goodbyes are said and Sadiebelle and Nana Philly reconcile their relationship. In the end though Pork Chop comes bearing bad news, Archie is gone on a boat to Cuba and stole Turtle’s share of the treasure while he was at it. Sadiebelle breaks down at the news and its in the end there as everyone is trying to cheer her and Turtle up that Turtle decides to stay in Key West with them. The book ends with her commenting about how lucky she was to have these people as her family.