In the early 1950s in Los Angeles, LAPD Sergeant Edmund "Ed" Exley (Guy Pearce) is resolute in his effort to uphold the legacy of his father, the renowned detective Preston Exley, who met a tragic end at the hands of an unidentified assailant he dubbed "Rollo Tomasi." Isolated within the precinct due to his keen intellect and ambitious drive, Exley chooses to testify against his fellow officers in the infamous "Bloody Christmas" incident, believing it will aid his promotion to Detective Lieutenant, much to the dismay of precinct captain Dudley Smith (James Cromwell). His strict adherence to the law prevents him from manipulating evidence, even when faced with a clear case against a suspect.
Contrasting Exley's principled demeanor is plainclothes Officer Wendell "Bud" White (Russell Crowe), who passionately seeks to punish those who harm women. His disdain for Exley is palpable, stemming from the fallout of Exley's testimony that led to his partner, Dick Stensland (Graham Beckel), being dismissed from the force. As crime boss Mickey Cohen (Paul Guilfoyle) serves a lengthy sentence, Smith enlists White's brutish methods to intimidate possible intruders looking to establish a presence in the city.
During his investigations, White crosses paths with Lynn Bracken (Kim Basinger), a high-class hooker who bears an uncanny resemblance to actress Veronica Lake, along with former police officer Leland "Buzz" Meeks (Darrell Sandeen). Both are connected to businessman Pierce Patchett (David Strathairn), who operates an escort service that transforms prostitutes into Hollywood star lookalikes via plastic surgery.
On the narcotics end of things, Sergeant Jack Vincennes (Kevin Spacey) is known for moonlighting as a consultant for the hit series Badge of Honor. His tipster is tabloid publisher Sid Hudgens (Danny DeVito), who offers him leads on high-profile arrests for his own public spectacle.
As Exley digs into a robbery and multiple homicides at the Nite Owl coffee shop, where Stensland falls victim, he manages to apprehend three African-American suspects. Through clever interrogation, he coerces confessions that never mention the murders themselves. Meanwhile, White's pursuit leads him to rescue a white girl from the suspects, albeit with ethical compromises Exley vehemently opposes. Despite solving the Nite Owl case, the deeper they go, the more they uncover a web of corruption entangling them.
As the investigation deepens, White finds his life intertwined with Lynn, and they discover connections to Susan Lefferts (Amber Smith), another victim, showcasing the intertwining of lives in this dark narrative. A discovery of Meeks' body by White unravels a further layer of deceit involving drug trafficking. Exley later learns about the corrupt history between Meeks and Smith, fueling both tension and desperation among the officers.
Shocking alliances and dark secrets ensue when Hudgens orchestrates a scandal involving District Attorney Ellis Loew (Ron Rifkin) that ultimately leads to murder. A guilt-ridden Vincennes teams up with Exley as they follow a trail revealing Smith’s deep-rooted corruption, leading to an explosive confrontation that ends with vindication, albeit at a moral cost. Exley grapples with the chaos, ending in a showdown where he is forced to confront his principles.
The story culminates with Exley revealing the extensive corruption within the department to protect its image, resulting in accolades for him. As the dust settles, Exley watches Lynn and White drive away to a fresh beginning, leaving him to ponder the cost of justice in a city rife with darkness.
