"The Caveman's Valentine" is a terrible title for an intelligent movie. It sounds like some B-grade fright flick from the 1950s with screaming blondes in strategically torn outfits being abducted by ape men found living on an uncharted island.

As it turns out, this "Caveman's Valentine" is actually a provocative, stylized psychological thriller/murder mystery about a one-time musical genius long ago driven out of a normal life and into homelessness by acute paranoid schizophrenia.

Played with an astonishing array of nuance by cinematic chameleon Samuel L. Jackson, Romulus Ledbetter is a disheveled, massively dreadlocked, ranting but misunderstood madman. His mind has become a tangled, delusional plane where an unseen evil -- an omnipotent adversary with powerful ray weapons -- conspires against him to take over the world.

Now living inside a rocky outcropping in a park on the edge of Manhattan, Romulus (known as "the caveman" to locals) becomes entangled in a mystery that taxes his remaining sanity when the body of a drug-addicted young drifter is found frozen to death in a tree outside his cavern.

Romulus is convinced this kindred lost soul was murdered by a rich, highly controversial photographer (Colm Feore) known for his violent images that featured the dead boy as a model. But the police -- including his own daughter (Aunjanue Ellis) -- won't listen to his raving rationale. He pulls himself together enough to get cleaned up and re-enter the artistic community so he can gain access to the photographer's estate and investigate this unsettling death. But his erratic behavior puts him -- and everyone else -- at great risk.

Helmed by feature sophomore Kasi Lemmons, who made such a lasting impression directing Jackson in "Eve's Bayou," this film isn't as resonant and lucid as her last, but it's no less fascinating while in action.

Lavishly visual and enigmatically atmospheric (the camera often sees the world the way Romulus imagines it), "The Caveman's Valentine" is also blessed with impressive performances that make even incidental characters fleshy and multi-dimensional. Anthony Michael Hall is particularly good (and almost unrecognizable) as a wealthy Fifth Avenue benefactor whose curiosity and white guilt beget Romulus a shave, a hot bath and a new suit.

It's a good thing, too, that "Caveman" has all this going for it, because the strong acting and metrical filmmaking buy the picture several short reprieves from collapsing under the continued strain of gross implausibility.

I didn't buy that the rich guy's dubious wife would happily shave Romulus in one awkward scene, instead of him doing it himself. I scoffed at the photographer's quizzical sister (Ann Magnuson) taking Romulus to bed (although it hadn't occurred to me that she didn't know who he really was). But those problems I could shrug off.

The same cannot be said for the whodunit/how-it-was-done switcheroo finale -- an outcome so impossibly complicated and absurdly staged it would make even Agatha Christie laugh out loud.

This I blame on the script (adapted by George Dawes Green from his novel) because somehow Lemmons' skill behind the camera and Jackson's tormented performance make it worth sitting through just the same.