Rookie detective Keiko's (Hitomi) first case is a mysterious suicide of a young woman (a neighbor claims to have heard her screaming for help). When a man commits suicide in front of his wife seemingly while having a nightmare, Keiko ties the two deaths together when she discovers that the two victims phoned someone named "O" shortly before their deaths. Believing that O may have played mind games with the victims and abetted their deaths, the police attempt to capture him in a two-fold manner. They first plan to have a decoy contact the killer pretending to be suicidal and they then make use of the services of the reluctant and suicidal "nightmare detective" Kagenuma (Ryuhei Matsuda) a young man capable of entering peoples' dreams (usually with disastrous outcomes). When the decoy attempt proves unsuccessful, Keiko's partner Wakamiya (Masanobu Ando) calls and makes contact with the killer who suggests that the man is suicidal without even being aware. When Kagenuma is unsuccessful at preventing the killer from claiming Wakamiya, Keiko herself calls the killer but she may have to face off with him alone when a disillusioned Kagenuma refuses to continue probing people's nightmares.

Not as visually audacious as Tsukamoto's earlier films like A SNAKE OF JUNE and TETSUO, NIGHTMARE DETECTIVE looks more like his recent mainstream pieces such as VITAL although there is a continuity of themes beneath the surface of this NIGHTMARE ON ELM STREET-esque scenario. The killer's notion that modern people have lost the primal pleasure of living is related to the voyeur's motivation in stalking the repressed heroine of A SNAKE OF JUNE. A dark thread of humor (made less subtle in the English dub) leavens the sometimes banal rendering of urban loneliness and despair (such as shots of urban cityscapes underlined by hundreds of overlapping voices making angry, sad, frustrated, and suicidal exclamations). While Matsuda is an enervating hero, Hitomi gives a good performance despite being saddled with the usual vague haunted past that motivates most movie characters to join the police force. The nightmare effects are not particularly original but the plotting keeps the film distinct from other cellphone-obsessed J-horror films. In 2008, Tsukamoto made a sequel to NIGHTMARE DETECTIVE with Matsuda reprising his lead role.