Looking forward to a two-week fishing vacation, Doug and Helen Stilwin and their son Bobby drive across the Mexican border and head down the coastline. On the winding, isolated road past Ensenada, they are stopped at a police roadblock, then waved on. As they drive away, Doug reveals that he has brought his old army pistol along for target practice. Eventually, the Stilwins reach the deserted beach where Doug used to fish with his buddies when he was in the Army. While Bobby is exploring the rickety jetty, his foot gets stuck between the boards, and Doug goes out to help him. Bobby makes it safely back to the beach, but a plank collapses and sends Doug crashing to the ground. Before he can move, a piling breaks and lands on his lower leg, pinning Doug to the rocks underneath. Helen and Bobby try various means of dislodging him, but the piling cannot be moved. Thinking they might be able to pull the piling off if they could tie it to the car, Doug suggests that she return to the deserted ranch where they had stopped for water earlier and look for a heavy rope. With an estimated four hours to go before the tide reaches Doug under the pier, Helen sets off for the ranch, leaving Bobby with his father. After a harrowing drive, Helen reaches the ranch. She breaks into the tool shed and has just found a rope when she notices an American man standing outside. She asks him for help and quickly drives away with him, unaware that he is leaving behind the concealed body of a murdered man. On the road, the taciturn stranger, Lawson, finds Doug's gun in the glove compartment and threatens to kill Helen if she does not cooperate with him. They are soon stopped by police officers, who are searching for a dangerous escaped criminal, but Helen, with the gun pressed into her side, can say nothing. When the police go, Lawson takes the wheel but refuses to take Helen to her family. They soon approach another roadblock, and when Helen tries to escape, Lawson drives through, with the police in pursuit. One of the tires blows out, and while Lawson is changing it, Helen notices the prison number on the back of his shirt. Meanwhile, at the beach, Doug and Bobby try unsuccessfully to flag down a passing ship as the tide gets higher. Back on the road, a police car approaches Helen's car and fires at the fugitive, but Lawson escapes. Aware that police cars travel in pairs, Lawson decides to lay low for a while, and they pull off the road. Helen tries to convince Lawson to go to the beach by offering him Doug's clothes and identification papers, and suggestively tells him she would do anything to save her husband. Lawson agrees, and they arrive at the beach as the tide is getting dangerously high. Lawson tries attaching a rope to the piling and towing it off with the car, but the heavy timber will not budge. Undeterred, Lawson resourcefully uses a board to get leverage, and Helen manages to free Doug just as the rope breaks. With Doug safely resting on the beach, Lawson reminds Helen of her promise to go away with him, but when she stoically agrees, he is so impressed by her spirit and dedication to her husband that he simply says goodbye. Before he gets into the car, they notice one of the tires is flat. As the sound of police sirens grows near, Helen and Lawson shake hands, and he escapes under the pier. Alone with her thoughts, Helen muses on the choices she has made.