The film stars Kevin Kline as Nick Starkey, a smart ex-New York City police detective who is lured back into service by his police commissioner brother (Harvey Keitel) when a serial killer terrorizes the city. Nick becomes involved with the mayor's daughter (Mary Elizabeth Mastrantonio) and is aided in his investigation by his neighbor, an artist played by Alan Rickman.
On New Year's Eve, Manhattan socialite Alison Hawkins returns home from the evening's festivities. As she feeds her fish before going to bed, she is strangled to death by an undetected intruder with a blue ribbon. It is the latest murder by a serial killer who has been terrorizing New York for 11 months.
New York Mayor Flynn is frustrated with the lack of progress in tracking down the killer, and tells NYPD commissioner Frank Starkey to "get [his] brother, and get him now," as they both know Nick is the only man brilliant enough to catch this killer. This is a controversial assignment for Frank, as two years ago, Nick was disgraced in a scandal, and expelled from the force. Frank goes to the scene of a raging fire to find Nick, who has become a firefighter. Frank talks Nick into returning, but only on the condition that he be able to cook dinner the next night for Frank's wife, Christine, who is Nick's ex-girlfriend. After a press conference announcing Nick's reinstatement, Christine and Nick have dinner. Old wounds are opened, including mention of a canceled check that had been evidence that Frank was involved in the scandal that got Nick fired.
Police Captain Alcoa is not happy with Nick's return, having despised his attitude but respected his abilities as a detective, but has to go along with the mayor's demand that he give Nick anything he needs to solve the case. After reporting for work, Nick takes a different office than the one he was assigned because the light was not to the liking of his painter friend, Ed. After getting Alcoa to add Ed to the payroll as his assistant, Nick begins work on the case. His first lead is to speak to the mayor's daughter, Bernadette, who was a friend of Alison Hawkins. After Nick and Bernadette visit Alison's apartment, Nick decides to let Bernadette stay at his apartment, because she is too frightened to return to her own.
Nick realizes that all of the 11 previous murders occurred on dates that are prime numbers, all of which are among the 12 prime numbers possible up to the number 31. Because 5 is the only one of the 12 prime numbers that has not been used, he knows that the next murder will take place the next night, the fifth of the month.
Nick appears to have been proven wrong when a woman is strangled one day ahead of Nick's prediction, after which the killer leaps out the window to his death. Nick believes that this is a copycat killing, especially when he learns that the man broke a window, as opposed to picking a lock to gain entrance as in the other murders. To Frank and Flynn, however, it is a closed case, and they are content to be done with Nick.
Nick and Ed figure out that the position of the victims' buildings, when seen on a map of Manhattan, forms the constellation Virgo. They also realize that all the rooms in which the murders took place have windows on the front of the building, and that when the exterior positions of the windows are lined up together according to which floor they are on, they correlate to 11 notes in the chorus of the song "Calendar Girl". This enables them to identify where "The January Man" will next strike.
Nick sets a trap with Bernadette as bait, outfitting her with a neck guard to prevent the killer from strangling her. The trio stake out the room in a supply closet and witness the killer picking the lock to get into the apartment. They intercept the apartment's resident and send Bernadette in, where she is attacked. Nick breaks in and, after a prolonged struggle with the killer, subdues him. He then wraps him up in the hall carpet and delivers him to the police outside the building.Kevin Kline as Lt. Nick Starkey
Susan Sarandon as Christine Starkey
Mary Elizabeth Mastrantonio as Bernadette Flynn
Harvey Keitel as Commissioner Frank Starkey
Danny Aiello as Capt. Vincent Alcoa
Rod Steiger as Mayor Eamon Flynn
Alan Rickman as Ed
Faye Grant as Alison Hawkins
The movie received negative reviews from critics. Roger Ebert, of the Chicago Sun-Times called it "one of the worst movies of all time," writing: "The January Man is worth study as a film that fails to find its tone. It's all over the map. It wants to be zany but violent, satirical but slapstick, romantic but cynical. It wants some of its actors to rant and rave like amateur tragedians, and others to reach for subtle nuances. And it wants all of these things to happen at the same time." Rita Kempley of The Washington Post was even more harsh, writing, "Eliot called April the cruelest month, but then he hadn't seen The January Man. Billed as a mystery with romance and comedy, it is a damp sock of a movie that makes you wish for a leap year".
The film's box-office gross (in the USA) was $4,611,062. It holds a 21% rating on Rotten Tomatoes.