14 year-old Ellis lives on a makeshift houseboat on the banks of a river in Arkansas with his parents, Mary Lee and Senior. He sneaks out early one morning to meet his best friend, Neckbone.
Neckbone, also 14, lives with his uncle, Galen, who makes a hardscrabble living diving for oysters. The two boys set out to an island on the Mississippi River, where Neckbone has discovered an unusual sight-a boat, suspended high in the trees, a remnant of an extreme flood sometime in the past.
They climb the tree and into the boat only to find fresh bread and fresh footprints. Realizing that they are not the only ones who have discovered the treehouse boat, they decide to leave.
When they reach the shore, they find the same footprint in their boat. And that's when they meet Mud. Mud is a gritty, superstitious character; his clothes are dirty, his tooth is cracked, and he needs help