In Arkansas, 14-year-old Ellis lives in a floating house with his mother Mary Lee and his father Senior. Ellis helps his father selling fish with his best friend Neckbone. Ellis and Neckbone find a motorboat stranded on the top of a tree in an island on the Mississippi River since a flood and they plan to fix the boat for them. One day, they climb the tree and they find fresh meal inside the boat meaning that someone is living in "their" boat. They leave the place and meet a man named Mud near their boat.