Marleau works as a night watchman in a large film production studio: Popcorn International. The job suits him because a failed acting career left him with a bitter taste. Marleau desires nothing more than tranquility and anonymity.
The fates have other plans when a mysterious individual begins to assassinate the bosses of Popcorn International one by one, announcing each crime with a melancholic trombone tune. What have these men done to deserve such vengeance?
Marleau must discover the truth quickly, as the assassin leaves incriminating clues on each corpse, pointing towards him. To make matters worse, his daughter Josée, a tech-savvy teenager, visits him and becomes convinced that she alone can save her defeatist father.
Meanwhile, police inspector Graselli sees an opportunity for advancement and glory in a case that should bring him both.