This is a weird movie, in that there is a creative conflict between the director, Jean-Pierre Melville, and Jean Cocteau, the author of the novel and the screenplay, and the voice-over narrator.
Melville is responsible for some beautiful filming - the schoolboy fight at the beginning, the murder at the end - and though the material isn't his own, quite clearly it fits in with his recurring themes of loyalty and betrayal. He gives the film a narrative fluidity and grace.
What Cocteau brings is his usual self-pitying, pretentious narcissism, and his patronising attitude to his audience, which he regards as having to have everything spelt out to it. This is reflected in his voice-over, a thin, reedy hectoring voice which keeps telling you things you have already seen or already know.
The ultimate narcissism is in the casting of the Edouard Dermithe as the doomed sickly brother, Paul. Dermithe is a Cocteau regular, bears an alarming resemblance to him, and was eventually adopted as a son by him, although the triangle between the two of them and Cocteau's long-term lover Jean Marais was a lot more complicated than that suggests. Here he plays the oldest 16-year-old in the business.
He is matched by Nicole Stephane as Elisabeth, nearing 30 at the time she is meant to be the other orphaned teenager. The two of them play the kind of games better portrayed by those other two psychopathic siblings, Bette Davis and Joan Crawford, in "Whatever Happened to Baby Jane?". They are equally hammy, but without the camp relish of Bette'n'Joan.
The whole thing takes place in a kind of hermetically sealed unreal world where the kindly doctor pays for all their care and upkeep (wish my doctor did that!) and takes place in a huge renaissance chateau, rarely going outside. Other characters intrude on their private world. When Paul falls in love with Agathe (Renee Cosima, who also doubles as the rebellious schoolboy Dargelos), Elisabeth first lies to divert their affections, and then when her deception is discovered, kills Paul rather than give him up, before killing herself.
This is the stuff of penny dreadfuls, and the posturing philosophising Cocteau lays over it ("You need to be so bad life spits you out") doesn't disguise the thinness of the material.
Melville makes it seem better than it is, and we are at least blessed with one of the most powerful images in movies right at the end, as Elisabeth falls back through the fan-like screens. The image is emblematic of the whole movie, which is beautiful without substance.