In a small Parisian building, a diverse group of people crosses paths, likes and observes each other, without always seeing each other.

Prudence and Bélisaire Beresford have decided to take things easy. But when a rich Russian heiress disappears, Prudence can't resist and Bélisaire is forced onto the adventure. Their investigation will put them on the trail of a mysterious scientist who holds the secret to eternal youth...