However, just because we don't know who committed the two murders until the end, this doesn't mean Chabrol is only interested in artifical games. The limits of the whodunit paradoxically give Chabrol the freedom from delineating the psychology of the criminal, to something much more interesting to him; in other words, the unknowability of other people, especially those we love, live with and think we know best.
Chabrol's films are so self-contained and remote, that it's rare to find him concentrating on 'topical' issues. Here the subject is the all-too-familiar paedophile rape and murder of a young girl in the woods. She was last seen at a lesson with her art teacher, Rene, and suspicion immediately falls on him, in one of those oppressive small towns where the Internet will never outpace malicious gossip. If we didn't know whodunits, we might think so too - he is lame, shifty looking, whiny, and a failed artist experiencing mental breakdown who thinks his masseuse wife, Vivianne, is having an affair with a slick media personality, G.R.
There are other suspects: G.R. himself, his criminal go-between, and Rene's friend, Regis, even, as the coroner cheerfully suggests, a woman with strong hands and gloves - an exact description of Vivianne earlier. But it is Rene everyone suspects, especially the new Chief Inspector, Lesage, whose personal stake in the case (she has a daughter of the same age as the dead girl) makes her determined to bring him to justice.
'Mensonge' is a psychological study in the guise of a mystery thriller. We are asked to follow Rene's reactions to the murder, social ostracism, artistic failure etc., and yet we're not told whether he's the murderer or not, or any of the other characters, which would surely be a crucial element in anyone's psychology! so these two impulses - towards psychological truth and towards a mystery story which necessarily precludes the audience having any access to the character's psychology, puts it with the same level of knowledge of characters as the other characters, making for an effectively tense film, which, beyond its mystery trappings, asks whether we can ever know anyone, when trust, or self-confidence, or faith in 'reality' is gone.
The film links the idea of lies (characters concealing truths, making realities out of lies), with art (painting - Jacques revels in panoramas and trompes d'oeil; the second murder is 'composed' like a painting). Throughout, various media for the diffusion of truth - painting, TV, books, recitals - as well as the police investigation, with its need for artistic resolution, are highlighted, interrogated and undermined (even a last minute confession is suspect, and the denouement, appropriately, takes place in a deep mist). Chabrol's blithely elliptical narrative style further compounds our uncertainty. As with every Chabrol, the surface every character sees, or creates, is as treacherous as a trompe d'oeil. As the child-murder in the forest, echoing 'Diary of a Chambermaid', suggests, Chabrol is letting out the closet Surrealist in him.