The Man in the Basement

Simon and Helen live in Paris together, they decide to sell a basement in their building. The man who buys it has a troubled past and the couple's life is turning upside down.
A Parisian couple decides to sell an unsanitary basement in their building. A very ordinary, nondescript man, Mr. Fonzic, shows up to buy it. Nothing unusual there, until the man moves into the cellar and makes it his permanent residence. The couple tries desperately to cancel the sale but to no avail. Worse, Mr. Fonzic becomes a threat to their family as he befriends their teenage daughter on whom he seems to exert a perverted influence.