Nicole has tired of Michel's cruelty, and she sympathizes with perpetually anxious and indecisive Christina. Nicole convinces Christina to kill her husband, and they concoct an elaborate plot. This is pulled off with the usual moments of suspense, when their plan seems likely to be foiled but remains undiscovered. Things become particularly intense when a retired detective (Charles Vanel) takes a strong interest in the case, and appears particularly suspicious of Nicole.
How others will see it. Diabolique was internationally acclaimed, and has remained influential and popular. It is ranked within the imdb.com Top 250, not bad for a film from the 1950s, and a Hollywood remake was released in 1996. Diabolique is deeply cynical, and those who know its ending and see it again often take pleasure in the suffering of Christina, who is manipulated into the most foul crime and is then tormented with guilt.
Fans of the film ignore the problems with the requisite final reel twists, which will be discussed shortly. It is easy to accept the world that a film creates, and even experienced film viewers sometimes forget that a black comedy posing as a murder drama works best if it remains plausible.
How I felt about it. Alfred Hitchcock attempted to buy the rights to the source novel, and Diabolique has the feel of a Hitchcock film. There's murder, a surprise ending, and numerous moments of suspense. Blatant comedy is introduced with the character of Herboux (Noel Roquevert), a fussbudget with a silently disapproving wife. All that's missing from classic Hitchcock is the subplot of a man wrongly accused of murder, and his inevitably successful romance with the film's hottest babe.
Certain Hitchcock films have their outrageous endings, such as Dial M For Murder. But Dialoque tops Hitchcock with two preposterous endings. This is where spoilers make their appearance, so you should avert your eyes now if you actually believe your life will otherwise be ruined forever.
It turns out that Michel wasn't killed after all. He conspired with Nicole to fake his death and apparent resurrection. The scheme was to fill Christina with such guilt and fear that she has a fatal heart attack. She will then be out of the way, so Nicole and Michel can marry and live wickedly ever after.
There are problems with this ending. It is dangerous, uncomfortable, and inconvenient for Michel. He could easily drown, or be forced to come up for air and reveal the subterfuge. The plan is overly complicated, probably illegal, and it may not work. Christina is unlikely to agree to kill her husband to begin with. She is also unlikely to die of a heart attack under any circumstances. Such things happen in movies more than in real life. And why would Nicole go through such things for Michel, who has no redeeming qualities. She's been around and knows better.
A second ending involves the detective confronting our wicked lovers and informing them they will go to prison. Although for what crime it isn't stated. Scaring someone to death might be difficult to prosecute. This is a pat ending compelled by the Production Code, which in its day insisted that the guilty are always punished.