In a bar in France, a lonely English academic on holiday meets his double, a French aristocrat who gets him drunk, swaps identities and disappears, leaving the Englishman to sort out the Frenchman's extensive financial and family problems.

The family's glassworks is losing money and faces closure, so John renegotiates a contract to keep it afloat for six months.

The next day he learns Françoise's dowry is in trust for a male heir, but if she dies or reaches the age of 50 without having had a son, Jean will inherit the money instead.

In the nearest town, John meets Béla, another of Jean's mistresses, who becomes suspicious of his sudden concern for the family and its business.

When she's found in the well at the glassworks, John discovers that Jean murdered Duval and threw his body in the well, accusing him of being a Nazi collaborator.

The next day, John gets a telephone call from the real Jean de Gué, who says he will be back in the evening and will meet him at the glassworks.