Commander aboard a supertanker, Marco Silvestri must return urgently to Paris. Her sister Sandra is in dire straits: her husband committed suicide, a bankrupt business and her only daughter adrift. Sandra points to the culprit: businessman Edouard Laporte. Marco rents an apartment in the building where Laporte has installed his mistress and their son. But Marco had not foreseen the secrets of Sandra, which confuse the situation ...