Time Out says
They're perfect for each other. That's what you think the first time expat Czech professor Adam Belinski (Boyer) and mercurial plumber's niece Cluny Brown (Jones) encounter each other in pre-WWII London over a stopped sink. She loves to work on pipes, and it's clear from their delicious banter that he'd like her to work on his (forget double, the entendres here are practically quadruple). But first they have to take a feature-length detour through respectable society---to try to find, as Cluny so (mock?) virtuously suggests, their "place" in the world.
Off, then, to a country mansion filled with people who know their place; where Belinski charms himself into the upper crust and Cluny, by chance, is taken on as a servant. But try as they might, free spirits like these can't be tamed---it doesn't matter how many maids' outfits they squeeze into or anti-Hitler political stances they trade on. The famed Lubitsch touch (courtesy of director Ernst, helming his final production) keeps things light and frothy, even as some of the story's knottier themes pierce you to the core; at its heart, this is a tale of two misfits gallivanting through a world about to go mad. So go feed some squirrels to the nuts. This is as good as movies get.