It is the height of the fashionable season and the world-famous singer, Anita Stella, comes to Cannes on the Riviera, where she has been engaged to perform at a Charity Ball sponsored by society leaders. John Egan, a distinguished British diplomat, traveling incognito as Baron Dupont, for reasons of State, falls in love with Stella and resolves to make her acquaintance. Egan/Dupont persuades a waiter, George, at the ball to exchange clothes with him and is brought into proximity with Stella. Meanwhile, Mary, a pretty tap dancer arrives in Cannes, seeks out the supposed Dupont and introduces herself as his long-lost sister. To protect himself, Egan/Dupont is compelled to acknowledge the relationship, but Mary is really an impostor playing a game of her own with her accomplice George the waiter. Later,a diamond necklace is stolen from one of the guests at the ball, and the distinguished British diplomat, who can also tap-dance, finds himself as the primary suspect.