Having fortuitously discovered a photograph in which Marthe embraces someone unknown, Étienne Dorsay becomes jealous and imagines various stratagems to identify the lover. In the meantime, he and his friends acquire a weekend house for a very low price.

The film follows four families, with different nationalities (French, German, Russian and American) but with the same passion for music, from the 1930s to the 1960s. The various story lines cross each other time and again in different places and times, with their own theme scores that evolve as time passes. The main event in the film is the Second World War, which throws the stories of the four musical families together and mixes their fates. Although all characters are fictional, many of them are loosely based on historical musical icons (Édith Piaf, Josephine Baker, Herbert von Karajan, Glenn Miller, Rudolf Nureyev, etc.) The Boléro dance sequence at the end brings all the threads together.

Minister Melone, his mistress, and his bodyguards, before heading to Luxembourg to drop off a briefcase filled with embezzled money, stay in a hotel. Lord and Lady Duncan also arrive, welcomed by Sophie, daughter of Professor Moricet, an eminent weapons researcher. They are at a show where a strange couple is watching them... Moricet is kidnapped with his briefcase containing top secret plans. From then on, detectives, briefcases, spies, and guards intertwine in a relentless and eventful pursuit! Which of them will recover the 'real' briefcase?