One day, Paul Mallard, a small employee without history, learns that Jenk (Gérard Depardieu), a man accused of having killed an old man with a hammer, will be hanged. The criminal claims to have met a certain Polo at the time of the crime, which would prove his innocence. Paul sees this as a chance to be famous...

Jenk is released, and he immediately settles in Paul Mallard's house, blackmailing him on his false testimony. He completely takes over the little man, becomes demanding, threatening... Basile, Paul's brother is irritated by his brother's sudden celebrity.

Jenk terrorizes Paul on a daily basis. His violence increases every day, and he has resumed his shady activity... Paul can no longer bear it. But how can this placid little man defend himself against this criminal ?