Director Claude Chabrol’s 50th feature, “The Flower of Evil,” is a voyeuristic puzzle. While he opens up the dark secrets of an upper-class French home for all to see, and everything is plainly visible, nothing is really revealed. In this house where the wallpaper matches the headboard which matches the comforter which matches the curtains, in this house where incest and murder go hand-in-hand, there looms a ruin. The occupants know it is coming, but we voyeurs are left in the dark until the very end.

Chabrol smears the house with blood from the very beginning, floating the camera like a bubble up the stairs and into the master bedroom where a dead body awaits. Then on to the story with no mention of placement in time because, as we are told later, there is no future or past, there is only the continuous now. And now Anne Charpin-Vasseur (Nathalie Baye) is the matriarch of the household and she is running for mayor. She seems pleasant enough, but her husband Gerard (Bernard Le Coq) completely loathes her. Meanwhile Gerard’s son Francois (Benoit Magimel) has just come home from Chicago and it is quite clear that he has a crush on his stepsister, Michele (Melanie Doutey), whom he has lived with since he was little. This crush very quickly leads to sex facilitated by Aunt Line’s (Suzanne Flon) loan of a country house. Clearly Aunt Line, Michele’s grandmother, sees something of her old love for her fraternal brother, who was killed by the Nazis, in Michele’s and Francois’ love.

Under the wings of Ms. Flon’s superb performance, the other actors are allowed to flourish. She never intrudes upon a scene, but works quietly in the background, as Aunt Line likes to make everyone else happy while abstaining herself. She inhabits the role of that favorite, totally supportive grandmother. But underneath Aunt Line’s cheek-to-cheek grin is an overwhelming sadness, caused by her Nazi collaborator father, which leaves her hardly able to hold up her plastered facade. Yet her character has more depth. She has great spirit which carries her through the eternal present and brings her some genuinely happy moments in her sadness. Ms. Flon lets us discover all this on our own; she never forces her performance.

Completing the trinity of great performances are Magimel and Doutey, who have created some of the creepiest, sexiest moments on camera to date. Francois is completely in the power of Michele’s sensual flirtations and he gives himself up to her in every kiss. When she kisses him it is as if every bit of resistance, of intelligence has been drained out of Francois and replaced by lust. And you can see in Michele’s face that she knows this and gets off on it. The fact that they are brother and sister in spirit further emphasizes their loss of control. Watching the two of them is the ultimate act of voyeurism and greatly adds to the erotic, carnal, uncomfortable nature of these scenes. All of this is entirely due to Magimel’s and Doutey’s uncommonly keen sense of their bodies, down to the smallest sensual movement.

But while it is watchable, “The Flower of Evil” isn’t riveting. In essence, it actually comes off as frustrating and its characters as vaguely annoying. But this frustration is clearly intended by Chabrol, and the characters are only annoying because he never quite gets as deeply into them as the film’s voyeuristic feel seems to promise he will. It seems “The Flower of Evil” is a postmodern “House of Usher” where the fall occurs somewhere behind the scenes and we are left to uncertainly figure everything out only to discover that there is no real fall at all.