François Truffaut's La Sirène du Mississippi (1969)

Truffaut adapted this film from William Irish's thriller Waltz into Darkness (1949), which would have been a good title for this film.¹ But if you're going to use another title, why not give a proper translation of 'Sirène' here: not as 'mermaid', which suggests a pleasant creature, but as 'Siren', which indicates that you're dealing with danger: this is about another of Truffaut's femmes fatales. When Louis Mahé (Jean-Paul Belmondo) meets 'Julie Roussel' (Catherine Deneuve) in Réunion off the boat from New Caledonia he is in serious trouble, expecially as he is immediately smitten by this beautiful young woman he is to marry when he expected to find a rather plain woman: they had been corresponding following a small ad in a newspaper.

'Julie' lies about the photo she sent Louis (which is a lie in itself as she never sent it), and Louis admits that he too lied about being the foreman of a cigarette factory and plantation when he's in fact the owner. They're swiftly married, Louis (without even thinking) puts his wife's name on his personal and business account, and by the time Berthe (Nelly Borgeaud), the real Julie's sister, wonders why she's not heard from her, the false Julie has run off with Louis's money. Berthe and Louis hire a private detective, Comolli (Michel Bouquet) to trace 'Julie'.

Louis flies to France and by chance – one of those remarkable coincidences frequently found in films – discovers she's working in a night club in Antibes. Louis finds her – her real name is Marion Vergano – and is prepared to kill her but she wins him all over again, relating her poor childhood, telling him her lover Richard killed Julie, and she has no more money. Hiring a house for them near Aix-en-Provence Louis – in another of those coincidences – runs into Comolli, gives him the slip, but when he turns up at the hired house determined to find Marion, Louis is forced to kill him. Louis and Marion flee to Lyon, Louis briefly returning to Réunion to buy himself out. At a café in Lyon though they discover from a newspaper that a flood has uncovered the body and they are being sought: a small ad in a paper began the relationship, and it seems that a front page headline will end it. And they can't return to their accommodation to retrieve the money as the place is crawling with cops.

They escape to a chalet² where Marion – the two of them having almost no money left – begins to kill Louis with rat poison, which he realises and tells her he's not worried about dying for her, whereupon she relents and the audience last sees them walking from the chalet in the snow, presumably towards Switzerland.

¹ In 1968 Truffaut had adapted Irish's novel The Bride Wore Black (1940): this time a literal translation.

² The chalet is the same one used in Tirez sur le pianist (1960) in Le Sappey-en-Chartreuse, Isère. It was also used in Bertrand Blier's Buffet froid (1979).