A Boston couple, Gail (Meryl Streep) and Tom (David Strathairn) are having marital problems. Gail, a rafting expert, decides to take their child Roarke (Joseph Mazzello) on a holiday rafting down the Salmon River in Idaho, along with their pet dog. At the last minute Tom joins them. As they are setting off they meet a couple of other rafters, Wade (Kevin Bacon) and Terry (John C. Reilly), who appear to be friendly.
After a day's rafting the family make camp for the night, but Tom continues to work on his laptop computer rather than enter fully into the experience. The family are joined by Wade and Terry who help to celebrate Roarke's birthday. Gail flirts with Wade. However, after a while Wade begins acting suspiciously and Gail decides it would be best to part ways. During the morning's rafting Wade reveals to Roarke that they have a gun with them. As they raft down the river the parents discuss an exit strategy that will allow them to leave the two men behind, and at lunch they attempt to leave on their raft and get away before Wade and Terry realize what is going on.
Their attempt fails and Wade pulls the gun on them and assaults Tom. Gail then realizes that an armed robbery she had heard about was actually carried out by Wade and Terry, and their rafting trip is actually a way for them to get away. The family are forced to raft at gunpoint down the rest of the river before they all set up camp for the night. During the night Tom attempts to steal the gun off the sleeping Terry but is heard and has to run into the bushes and to the river. Wade gives chase and believes he has shot him when he hears a loud splash into the water.
It's revealed that Wade and Terry, in order to aid their escape, want to go on down the river to a set of rapids where in recent years one person was killed and another was left paralyzed. Consequently, rafting is no longer allowed. Wade and Terry force the rafters down through the rapids despite Gail's repeated att