When Mrs Hudson's young nephew, Ralph, decides to go to Paris and become an artist, his mother is distraught. She enlists Mrs Hudson's assistance to try and persuade him to quit the fleshpots of that most debauched city and return home.
In Paris, the sisters soon find themselves caught up in the whirling fin-de-siècle world of bohemians and anarchists, the world of Montmartre and the Moulin Rouge. They encounter the likes of Toulouse-Lautrec, along with the fabled can-can dancer La Goulue and her partner Valentin the Boneless, among many other colourful characters. But then the discovery of the mutilated body of a beautiful young artists' model in the sinister catacombs of the city puts Ralph under suspicion of her murder...