The Joy of Singing (Le Plaisir de chanter) 

Muriel and Philippe work for an intelligence agency but also happen to be an unlikely pair of lovers. Their latest assignment is to recover a secret hidden by Constance, an attractive widow of a shady businessman. Constance, a calm and naive woman, attends an opera singing class. One by one Muriel, Philippe and an increasing number of other spies with bewitching voices sign up too. They all compete with one another, each trying to discover the pretty widow's secret.