As they are waiting for a divorce, young movie star Malissa Farrell and famous pianist Rudy Walter have left their baby, Johnny, with a child minder in Le Vésinet. Marinette, the latter's daughter, who has been assigned to return the young Dubois to his parents, mistakes Johnny for the other kid. As she can't find Mr. and Mrs. Dubois, Marinette entrusts Max, Mrs. Dubois' father and the drummer in Ray Ventura's orchestra, with the care of the baby. Max, who must join the other musicians in Monte Carlo, where the band is due to play for the Jazz Festival, has no other choice but to rake the little one along with him.
Source : IMDb