We who live in big cities know people who are not all there--not just neurotics (that's all of us) but neighbors, perhaps, certainly some of the homeless who are downright psychotic. We don't know what they see that we don't, but they appear to have rich fantasy lives, whether yelling at unknown enemies or huddled against a building talking to themselves. What some people don't realize is that most of these deranged people have perfectly lucid moments and some are even geniuses. (Excellent movie about the latter would be, of course, Philip Kaufman's "Quills" about the tormented Marquis de Sade who smuggles literary works from his asylum. and Scott Hicks's "Shine," about a brilliant pianist who has turned into a babbling idiot.) Geoffrey Rush, extraordinary in both roles, has nothing on our own Samuel L. Jackson, who in "The Caveman's Valentine" performs in the role of a luminous pianist-composer, formerly associated with the Juilliard school, who has become unhinged in the mind when he begins to hear voices from the fanciful Cornelius Gould Stuyvesant from atop the Chrysler building. Even more fascinating, he has sexual visions of dancers swirling about (captured wonderfully by Amelia Vincent's lens), seen either before or after his world turns sickly green--which signals the audience that he's about to go over the top, to do something unpredictable and mesmerizing.

Mesmerizing is the word to describe Samuel L. Jackson's performance in a film made by Kasi Lemmons, whose "Eve's Bayou" was named by Roger Ebert the best movie is its year. While the Kasi Lemmons touch is on display in this second effort, given the superstitions and voodoo that contributed to the gothic atmosphere of "Eve's Bayou," this movie most resembles Terry Gilliam's "The Fisher King," about a self- absorbed radio personality whose deep depression is lifted by a street person who needs rescue himself.

What drove this man, one Romulus Ledbetter (Samuel L. Jackson), off the deep end? Who knows? What turns a well- adjusted person into a paranoid schizophrenic is too complex a subject to tackle in a film or normal length. Instead, George Dawes Green, whose 1994 novle is the basis of his screenplay, appears even more interested in the rational motivations of the man than in his oddity. When Ledbetter-- whose lives in a cave and is ridiculed by the local yahoos-- discovers the inert body of a young man seemingly living in a tree, he rejects the police determination that the victim simply froze to death and is determined to investigate the case to win back the favor of his police officer daughter, Lulu (Aunjanue Ellis).

Believing at first that the victim was murdered by Ledbetter's archenemy Stuyvesant, he later comes to consider a high-profile artist to be the culprit. He suspects David Leppenraub (Colm Feore) of torturing the young man to death in order to evoke the needed emotions for his images. After penetrating the affluent world of a bankruptcy laywer, Bob (Anthony Michael Hall), who lends him a suit, he uses a contact to enter the domain of the artist and in the process has a sexual liaison with the artist's free-living sister Moira (Ann Magnuson). For a while Ledbetter's lucid moments enable him to deliver a sparkling rendition of a piano work by Terence Blanchard, allowing him time snoop around to discover clues that would implicate the arrogant artist in the murder.

"The Caveman's Valentine," then, is both a neo-gothic murder mystery and an exploration of the disturbed mind of a genius, each allowing the audience to thrill to the remarkable acting talents of Sam Jackson. Director Lemmons has covered the bearded Jackson in dreads down to his waist, eyes expressively bulging while he rants to strangers on the sidewalk yet talks softly to his daughter and to his imagined wife Sheila (Tamara Tunie). As though his frightening visions of dementia were not enough, Lemmons introduces quickly- edited black-and-white frames from Ledbetter's earlier and more down-to-earth life which are contrasted with the striking but undeveloped imagery from his unhealthy mind.

Though "The Caveman's Valentine" calls for quite a suspension of disbelief--positing that a rich lawyer and well- known artist would without hesitation invite such a disheveled man in their homes and that the sister of the artist would have no problem bedding the homeless man--the film rivets by Mr. Jackson's raw ability to convey the dimensions of paranoid schizophrenia, by the contrasting personality of the artist played with appropriate restraint by the talented Colm Feore, and by the regard that the imaginative Lemmons shows for movies as a visual medium.