Alex (Jean-Louis Trintignant) is newly married, and he and his wife are setting up housekeeping together in Paris. However, to complete their domestic arrangement, he must drive to pick up his new 12-year-old stepson Marc (Richard Constantini) from his school in Rome. The boy is extremely cynical and resentful at first, and when Alex states that their car is being followed, he doesn't believe it. However, events soon prove that Alex is correct, and their pursuit by an enraged psychopath becomes a terrifying duel to the death.