Jake Mason has always preferred the familiar. The twelve-year-old boy knows all the ins and outs of his hometown of Greenwood, and he likes knowing that he will always be able to hang out with the same friends every day. But all that changes when Jake and his family have to move due to his Dad's construction job. Now, not only does Jake have to adjust to a new school, but he also will have to deal with a whole different world when he meets Olivia Flynn.
Olivia is a girl who claims that a year ago, she traveled to a place called the Marshes of SanDango, where alligators and mosquitoes can talk and any adventure can happen. The problem is, no one else believes in the marsh's existence, and Olivia has recently begun to wonder if she had imagined the marsh. But when she meets Jake, Olivia decides that she wants to find out the truth about the marsh - by getting Jake to visit it with her.
Together the two kids not only meet alligators and mosquitoes with varying personalities, but they also have to face an empress and her army of snakes who want to take over the marsh. Along the way Jake and Olivia grapple with questions about who they are and what it takes to be a hero.