Alain Delon stars, as Jeff Costello is an assassin who lives a solitary life with no friends. Costello begins his new assignment stealing a car, obtaining new license plates and a gun from his associate. He then drives to a nightclub at night and shoots the owner, accidentally being seen by the club pianist Valerie (Cathy Rosier). The police pick up Costello and with the investigation led by a determined Police Inspector (Francois Perier), subject him and many others to a line up. Costello is released because he has set up an alibi with Jan Lagrange (Natalie Delon), and also because Valerie lies and states that she did not see him. When Costello goes to collect his money for killing the club owner, his employer attempts to kill him. Police Inspector (Francois Perier) puts together a team of undercover cops to trail Costello through the Paris Metro, an underground labyrinth where Costello escapes. Costello thus seeks to get paid for his killing job and get revenge on the shadowy businessman who hired him, and stay one step ahead of the police Inspector but makes a decision that brings about surprising results.
Question: Where does Costello escape the police?, Answer: The Paris Metro Question: What is Jeff Costello's profession?, Answer: Assassin Question: Who is the pianist who accidentally sees?, Answer: Valerie