Based on the novel Waltz into Darkness by William Irish (a pseudonym for author Cornell Woolrich), which was published in France under the title La Siréne du Mississippi, Truffaut's adaptation transposed the setting from the Deep South to the French territory of La Reunion and changed Irish's downbeat ending to a more open-ended fadeout, stating "You must never end a spectacle on a downward curve. Life may descend into degradation, old age and death, but a spectacle must exalt and uplift."
The story opens with Louis Mahe (Jean-Paul Belmondo), a wealthy tobacco plantation owner, becoming engaged to a woman, Julie Roussel, through a personal column in a newspaper. When Julie (Catherine Deneuve) arrives via the riverboat Mississippi, she does not resemble her photograph nor the woman he imagined from her letters. Louis is nonetheless enchanted by Julie's beauty and they marry. Then Julie vanishes mysteriously, absconding with all of the holdings in Louis's bank account. It is soon learned from Berthe Roussel (Nelly Borgeaud) that her sister is missing and that someone impersonated her on the arrival boat. Louis and Berthe hire a private detective, Comolli (Michel Bouquet), to apprehend the impostor and find the missing Julie. Later, Louis discovers his wife is in Antibes and tracks her to her hotel room where she confesses her name is Marion and was partner-in-crime with Richard (Roland Thenot), who robbed and murdered the real Julie. Louis, still infatuated with Marion, forgives her but soon the couple find themselves on the run from the police who want to arrest Marion for murder. It is only after the couple have fled to an isolated cabin in the French Alps that Louis discovers Marion's true nature.
According to Truffaut, Mississippi Mermaid was "above all the story of a degradation of love." He also said the "film had been offered to me two years previously with Brigitte Bardot. I had adored the novel, but I had said, 'Bardot, out of the question. It will be Catherine Deneuve or no one.' I waited patiently in the wings and, as soon as the rights were available, I bought them with money lent me by Jeanne Moreau...and I shot the film as I saw fit, good or bad..."
In Francois Truffaut: Correspondence 1945-1984, the director described his first meeting with Jean-Paul Belmondo who he had long wished to use in a film: "He [Belmondo] greatly liked the novel, the characters and the plot. The only reservation he indicated to me concerned the character's age, which is indeed more advanced in the book. I believe I set his mind at rest on this point by explaining to him how I saw things, and he then expressed his wish to make the film...I told him that the adaptation would follow the book quite closely and he showed no desire to delay his acceptance until he had read the script, which would in any case be physically impossible since we will have to begin pre-production in two weeks and I plan to write most of the dialogue during the shoot, as I have almost always done in my French films."
From the start, Truffaut had to balance the two acting styles of Belmondo and Deneuve who were quite different in their preparation. In an interview in The New York Times Truffaut said, "He [Belmondo] starts out in a comic vein and the disparity with what I want is so great that I tell myself, 'I'm going to have to explain this, it's going to be difficult, it's going to take a long time,' and not at all, he says, 'Oh, you want it sadder,' and within seconds he changes it completely. That's because he has the dual theatre-movie training. He knows how to emphasize a line and how to throw a line away, whereas Catherine Deneuve is exclusively cinematic, completely untheatrical, every intonation is even. So sometimes you have to say, 'This sentence is important': you have to bring her out. I think they go well together; they're good to look at. I made Mississippi Mermaid in Cinemascope, so I could have them both on the screen most of the time. In a lot of American movies with two big stars you have a problem of vanity; each star is filmed separately so you can put little lights in their eyes, and you get the impression they didn't act together. But I didn't want one to be more important than the other so I kept them together."
Truffaut's source of inspiration throughout the filming of Mississippi Mermaid was, according to John Wakeham in World Film Directors, "Jean Renoir, to whom the film is dedicated because...every time he got stuck with the improvisation, he asked himself how Renoir would have solved the problem. But notwithstanding the model, and ample allusions to the master himself - the thematic link with La Chienne , an open ending like La Grande Illusion , clips from La Marseillaise , and an allusion to Le Crime de M. Lange  in the title of a film within the film," Mississippi Mermaid also paid homages to writer Honore de Balzac, directors Nicholas Ray, Jean Cocteau and Alfred Hitchcock's Vertigo (1958), actor Humphrey Bogart, and a Cahiers Du Cinema editor whose name Comolli was used for the detective played by Michel Bouquet. There are even parallels and references to Truffaut's own work such as Shoot the Piano Player (1960) - the same mountain cabin hideout was used for the snowy climax in Mississippi Mermaid - and The Bride Wore Black (1968), which featured a heroine who was both a vision of beauty and a destroying angel to men, not unlike Deneuve's siren. (The Bride Wore Black was also based on a William Irish novel.)
Despite Truffaut's emotional and artistic investment in the film, the critical response to Mississippi Mermaid was decidedly mixed during its initial release. Variety reported that "Truffaut has come up with an uneven film mixing a love story, femme duality, suspense, but not quite getting the intertwining of wry tenderness, cohesive characterization and punctilious but charming insights that marked his recent pix." British critic Derek Elly wrote, "The director seems unsure whether to make a thriller, an homage, or a love story," but added that "beneath the trimmings, it is one of his most personal works...Truffaut's poem to the eternal bitch-goddess figure - and more particularly to Catherine Deneuve." (According to Truffaut's co-scenarist Bernard Revon, Deneuve was "the most beautiful love of his life.").
Truffaut was diplomatic about the criticisms, admitting that Mississippi Mermaid suffered a lack of cohesion because, for the sake of economy, he had to omit sections from the novel that would have added clarity and plausibility to the narrative and characters. He also realized that the casting of Belmondo and Deneuve created expectations in the audience that weren't met by his treatment of the material. "Perhaps what I had tried to do before in Tirez sur le pianiste [Shoot the Piano Player] and La Mariée était en noir [The Bride Wore Black] - combine an adventure story and a love story - worked less well here....as those who don't like it constitute 95%, I have to admit something went wrong."
Since its 1970 release, however, Mississippi Mermaid has been critically reappraised by many critics. David Thomson in The New Biographical Dictionary of Film wrote that it "actually masters Hitchcockian themes and turns into a rhapsody on a fatal obsession." And at a festival of Truffaut's work in 1999 at San Francisco's Castro Theatre, Edward Guthmann of the San Francisco Chronicle wrote "The decision to open the retrospective with "Mississippi Mermaid'' might seem odd, since the film was poorly received when released in the United States and has been held in such low esteem in the Truffaut canon...A classic case of a film being altered by overzealous cutting, ``Mermaid'' was released in the United States with 13 minutes missing. Now restored, those scenes give the film a clarity it lacked before and flesh out the characters in ways that justify their actions...The pieces all fit, and the result is a cool combo of film noir, star vehicle and picaresque romance. It's vintage Truffaut, and a great way to get acquainted or reacquainted with one of cinema's true masters."
Producers: Marcel Berbert and Francois Truffaut
Director: Francois Truffaut
Screenplay: Francois Truffaut; William Irish (novel "Waltz into Darkness")
Cinematography: Denys Clerval
Art Direction: Claude Pignot (Production Design, Set Decoration)
Music: Antoine Duhamel
Film Editing: Agnes Guillemot
Cast: Louis Mahe (Jean-Paul Belmondo), Julie Roussel/Marion Vergano (Catherine Deneuve), Berthe (Nelly Borgeaud), Landlady (Martine Ferriere), Jardine (Marcel Berbert)
C-124m. Closed captioning.
by Jeff Stafford
Truffaut by Don Allen
Francois Truffaut by Annette Insdorf Francois Truffaut: Correspondence 1945-1984 edited by Gilles Jacob & Claude de Givray
World Film Directors, Vol. II, 1945-1985 by John Wakeham