Ben Affleck as George Reeves and Robin Tunney as Leonore Lemmon in Hollywoodland

The movie begins in Beverly Hills on June 16, 1959, at the home of TV star George Reeves with a police investigation underway and Reeves' lifeless body on his bed. The police rule the death a suicide. The focus of the film then shifts to Louis Simo, a private investigator more interested in generating an income than in devotion to his clients. A man named Chester Sinclair is paying Simo to spy on his wife under the impression that she is cheating on him. Simo simply accepts his money and takes pictures outside of a building where she goes to from time to time. On a visit to see his son, Simo reacts to the boy's lackluster demeanor and asks his ex-wife Laurie what is wrong. She tells him it's because the actor who plays Superman has shot himself. Simo learns from a former colleague on the police force that the Reeves suicide has aspects that the cops don't want to touch. Simo, sensing the potential for making a name for himself, begins investigating the case and notes several apparent conflicts with the official version of Reeves' death. Simultaneously Simo bickers with Laurie over his failures as a father, particularly now when his son seems so troubled.

The film then shifts to flashbacks of Reeves' life, revealing Reeves to be a charming man whose acting career has stalled. At a nightclub, Reeves catches the eye of a beautiful woman and they end the night in each other's arms. In the morning a newspaper photo reveals to Reeves that the woman is Toni Mannix, the wife of Eddie Mannix, the general manager of MGM Studios. Frightened that an affair with a studio boss's wife will destroy what's left of his career, Reeves is angry that Toni didn't tell him. Toni, however, tells Reeves that she and Eddie have an open relationship and not to worry. The pair fall in love and the much wealthier Toni begins to buy Reeves expensive gifts such as a house, a car and jewelry. During their relationship Reeves gets the starring role in the television show Adventures of Superman. Reeves takes the job with humility, but continues hoping for more meaningful work, but now everyone takes him for a joke. As the years pass and Toni ages, Reeves becomes bitter at being a kept man and at Toni for not using her clout to help his career. He meets a young woman in New York, Leonore Lemmon, and leaves Toni for her. Toni is broken-hearted and furious, and Eddie seethes at her "mistreatment" by Reeves.

The film is redirected back to the life of Simo and his investigation of the facts of Reeves' death. Simo initially suspects that Leonore Lemmon might have accidentally shot Reeves during an argument, and in his imagination Simo sees that scenario played out. Then, thugs apparently working for Eddie Mannix beat Simo in hopes of scaring him off the case. This and other evidence lead Simo to suspect that Eddie had Reeves murdered and, again, Simo imagines what such an event might have looked like. Simo then learns that his client Chester Sinclair has murdered his wife because he got tired of waiting for information from Simo. A stricken and guilt-plagued Simo gets drunk and visits his son at school, but his inebriation scares the boy. Later, Simo visits Reeves's manager, Art Weissman. Weissman speaks highly of Reeves and his charm. He gives Simo a home movie Reeves had shot in hopes of promoting wrestling work. What Simo sees in the film suggests to him a sadness in Reeves, a weariness and humiliation with where his life has led. Simo's final imagined variation on Reeves's death concludes with the actor shooting himself. This is the most vivid of the three scenarios, with Simo imagining himself standing in the corner of the upstairs bedroom, and even making eye contact briefly with the weary Reeves.

The story of Reeves' quest for fame and success and Simo's realization of how that quest is paralleled in his own existence causes the detective to reevaluate his life. Simo watches another home movie, this one of himself and Laurie and their son in happier days. The film ends with Simo coming to Laurie's house wearing a suit and tie, and greeting his son hopefully.