A couple from Boston, Gail (Meryl Streep) and Tom (David Strathairn), are grappling with their marital issues. In a bid to reconnect, Gail, an experienced rafting enthusiast, decides to take their son Roarke (Joseph Mazzello) on an adventurous rafting trip along the scenic Salmon River in Idaho, bringing along their beloved dog. At the last moment, Tom decides to join them.
As they embark on their journey, the family encounters fellow rafters Wade (Kevin Bacon) and Terry (John C. Reilly), who initially seem friendly. After a fulfilling day on the water, the family sets up camp for the night; however, Tom becomes more engrossed in his laptop than in the experience. During the evening, Wade and Terry join them in celebrating Roarke’s birthday, which leads to some playful flirting between Gail and Wade. Yet, as the trip progresses, Wade's demeanor begins to shift, prompting Gail to sense that it might be wise to distance themselves from the new acquaintances.
The following morning, as they continue their rafting journey, Wade unexpectedly reveals a shocking secret to Roarke: they are armed. Realizing the imminent danger, Gail and Tom begin to devise a plan to leave Wade and Terry behind discreetly. However, their effort to escape is thwarted when Wade, brandishing the gun, menaces them, and Tom is assaulted. The nightmare deepens as Gail recalls an armed robbery that had occurred recently, now understanding that Wade and Terry have orchestrated this trip as a means of evading capture.
Under duress, the family is compelled to continue down the river at gunpoint, ultimately bedding down for the night. In a desperate move, Tom attempts to seize the gun from a sleeping Terry but is caught and forced to flee into the underbrush. Wade, suspecting foul play, blindly pursues him, convinced he has shot Tom after hearing a significant splash.
Wade and Terry's malevolent intent becomes more apparent when they reveal their plan to navigate a perilous section of rapids known for its dangers—an area where rafting is now prohibited due to fatalities. Ignoring Gail’s frantic protests, they push the family towards these treacherous waters, while a park ranger, who happens to know Gail, attempts to intervene. Unfortunately, Wade, cold-heartedly pointing his gun at Gail, ensures the ranger's cover is blown, leading to a tragic shooting that sees him plummet into the river.
In the climax of their ordeal, Tom reemerges just in time to flip the raft, leading to a tumultuous struggle for the gun that has slipped into the water. Following a heated confrontation with Terry, Gail bravely hurls the bag of stolen money overboard, disrupting their captors’ plans. The tension erupts as she turns the weapon on Wade, ending his threat as his body drifts away down the river.
The film concludes with the family, along with a now-arrested Terry, being airlifted to safety, having survived a harrowing experience that tested their resilience and will to protect each other.
