Harry Wethermill has fallen in love at first sight with the beautiful Celia,, a young woman of dubious background who has turned up in Aux-les-Bains as companion to the ostentatious, jewel-flaunting Madame  Dauvray – who is found  strangled in her sitting room – with no trace of the jewels. Wethermill and his friend Mr. Ricardo enlist the help of French detective Hanaud, in the hope of clearing Celia – but as the investigation progresses, it looks likely to seal her doom.