AustLit

A contemporary (largely negative) review in the New York Times offers the following synopsis:

'The movie begins familiarly, but potently, as Mr. Boyer, playing an international matchmaker, recruits some shrewd Riviera opportunists, headed by Mr. Ford, to spruce up a poor duke, Ricardo Montalban, as marital bait for Miss Lange, as the spoiled heiress.

'Mr. Ford is posted as a chauffeur in Miss Lange's villa. Guess what happens. And it takes a long, long time, with the incidents starting to meander at about midpoint. A seduction towards the end is laboriously coy.

'That sun-kissed scenery, though, should set anyone drooling, even as its wordliness magnifies the cardboard capering front and centre.'

Source:

'Screen: "Magnificent Sinner" Opens', New York Times, 25 April 1963, p.38.