The Joy of Singing.

A banker has died. He trafficked in nuclear material, so French intelligence assign two agents to find his list of contacts, which are on a flash drive: Muriel - the boss, acerbic, willing to sleep with any man, wondering if she should have a child - and Philippe, younger, boyish, meticulous, bothered by Muriel's frank sexual interest. They watch Constance, the banker's widow: a naïve, friendly, open, trusting. She's taking opera lessons, so the French spies join the class, which Muriel enjoys. It seems that other spies are after the same USB, and some of them sing as well. Singing, spying, and sex lead to duets of all kinds as well as to an eventual showdown.