Harry Baldwin, his wife, Ann, and their two children, 17-year-old Karen and 19-year-old Rick, leave their home in Los Angeles for a fishing trip. Two hours after their departure, they hear a tremendous explosion and learn that the city has been demolished by a nuclear attack. It soon becomes apparent that the greatest danger facing them is from the hordes of frightened looters running rampant. After deciding their safest course is to proceed to their vacation spot, they stop to pick up provisions and ammunition. When they reach their fishing spot, they set up home in a cave, where they will be protected from radiation. Nearby, three young hoodlums have taken over a farmhouse and are ravaging the countryside. They murder a couple who have followed the Baldwins to the area. Two of the thugs come upon Karen when she is alone and brutally rape her. They are shot by Harry and Rick, who also find that the youths have been holding a girl, Marilyn Hayes, as their prisoner. Taken to the cave, she is menaced by the third thug, but she takes Rick's rifle and kills him. When the radio reports that Los Angeles is safe, the family and Marilyn prepare to return to civilization and face the enormous task of rebuilding.