Six Days, Six Nights (1994)

Alice is a promising young artist in Paris. Her boyfriend Franck, a boxer, has just moved in to her attic flat. Then her sister Elsa, a bored housewife, leaves her unfaithful husband Thomas and turns up unannounced to stay with Alice and Franck. Elsa disrupts their life by playing psychological games with them, but they cannot bring themselves to throw her out.