JulienTavernier is a former paratrooper, who now works for millionaire arms dealer Simon Carala. He is in love with Florence, Carala's wife. The pair plan to murder Simon and make it look like a suicide, but Julien forgets a rather important detail. Leaving the engine of his sports car running, he races up to the office to retrieve it, but fate intervenes, and Julien misses his rendezvous with Florence. She spends the night wandering the Parisian streets alone. Meanwhile brash teenager Louis and his girlfriend Veronique decide to "borrow" the car, which launches a disastrous stream of coincidence with sinister consequences.