Of the 6 "Deutschefilm Klassiker" movies I bought so far, this one gave me most instant enjoyment, mostly because of the many scenes where the dialog is sharp and witty (in others, it's more conventional comedy). They made me laugh out loud so often - I'm not sure whether it fits the definition of "screwball", but I feel it must be close, especially in the American scenes.
Robert Ellin, a successful American composer/piano player finds his wife is cheating him, starts divorce proceedings and travels to Europe. On the plane he meets old buddy George Webb, whose career as saxophone player was ended by an accident, and now is airborne bar mixer (not for long - he gets fired for drinking on duty). To elope both his publicity and the detective his wife would put on his trail, Robert persuades George to swap identities, and gets to know Maria, a young but troubled bar manager.
I will not spoil what tribulations ensue, most are known from other romantic comedies, but it's less what they do but how they talk that pleased me so much - the witty script makes the actors really shine, from Gertrud Kückelmann to Curd Jürgens. I've seen both in other films of the early 1950s, where they did not leave such a very good impression on me.
I highly recommend "Musik bei Nacht" (an alternate title seems to have been "Liebes-Cocktail"), and the 2.99 euro our local Woolworth charges are very much worth it.