Years after serving together in the French Foreign Legion, American soldier of fortune Franz Propp (Charles Bronson) and French doctor Dino Barron (Alain Delon) are unexpectedly reunited under the most extraordinary circumstances.

Hoping to help a friend who has embezzled some bonds, Barron tries to break into a safe in the dead of night. Sneaking into an underground vault he is surprised to discover that his old pal Propp is also on the premises, likewise intending to crack the safe, albeit for his own benefit. Stuck together inside the locked vault they reluctantly agree to work together to escape, but will honour amongst thieves get them out of trouble with the law?