Jim and Huck have been on the river for a couple days, during that time, Jim built a tent on the raft to protect them against the weather. They eventually hit a big storm, and in the storm they come up to a shipwrecked steamboat, which Huck decides, against the wishes of Jim, to board the ship.
On the ship, Huck overhears the plans of two accomplices who plan to eliminate the third member of their gang. Huck then plans to release their boat, so that all three accomplices will be stuck on the sinking ship, however, when he goes to Jim, he discovers, that their boat has washed away, so they would be stranded on the ship.
Huck and Jim take off in the robbers ship, and eventually find their raft. Before that however, Huck told a watchman about the sinking ship, and that there were three people on the ship, and the Watchman reluctantly goes to find and save them.