Romulus Ledbetter (SAMUEL L. JACKSON) is a former Julliard-trained musician who snapped some time ago and is now a paranoid schizophrenic living in a park cave outside Manhattan. Everyone knows of Romulus, a.k.a. the Caveman, and his delusional ranting, including his daughter Lulu (AUNJANUE ELLIS), a city cop, and Sheila (TAMARA TUNIE), his estranged wife.
Thus, when Romulus truly finds the frozen body of Scott Gates, a homeless twenty-year-old, perched in a tree outside his cave, no one will buy into his theory that the person responsible is his omnipresent adversary, Cornelius Gould Stuyvesant, whom he believes watches his every move from atop the Chrysler building.
Although Lulu and the rest of the police believe that Gates simply froze to death, Romulus believes the man was murdered, a theory confirmed by one of Gates' friends, Matthew (RODNEY EASTMAN), a homeless junkie. It seems that Gates formerly worked as a model for acclaimed art photographer David Leppenraub (COLM FEORE), and after they had a falling out, planned to blackmail him with a tape allegedly showing the photographer torturing Gates. Accordingly, Matthew believes Leppenraub had Gates murdered, all of which feeds into Romulus' conspiracy-laden mind.
After briefly investigating the photographer and discovering they have a common acquaintance, Arnold (DAMIR ANDREI), Romulus borrows an old suit from a compassionate lawyer, Bob (ANTHONY MICHAEL HALL), and his wife Betty (KATE McNEIL), and then heads with Arnold to a fundraiser where Leppenraub will be appearing. There, Romulus not only gets to meet the photographer and play detective, but he also meets Leppenraub's sister, Moira (ANN MAGNUSON), and Joey (JAY RODAN), the young man who allegedly shot the torture videotape.
From that point on, and while dealing with various delusional visions - including those of odd emanations of light from the Chrysler building and a much younger Sheila who talks to him and acts as his muse - Romulus must overcome his own mental instability, and everyone's else's doubts about him and his theories, as he tries to solve the murder.