In 1977 Los Angeles, a young boy named Bobby admires a magazine centerfold of porn star Misty Mountains, when Misty herself crashes her car through the boy’s house and dies afterwards. Down-on-his-luck private eye Holland March (Gosling) is hired by Misty’s aunt, who claims to have seen her still alive. March’s investigation leads him to Amelia Kuttner, an associate of Misty’s who later pays enforcer Jackson Healy (Crowe) to scare March away. Healy barges into March’s house and breaks his arm before leaving.
Healy is interrogated by two thugs, “Blueface” — so named after he sets off a dye pack while searching Healy’s apartment — and Older Guy, about Amelia. Healy wards them off with a shotgun, and teams up with a reluctant March to find Amelia first.
March and Healy question Amelia’s anti-pollution protest group and meet Chet, who brings them to the burnt-down house of Amelia’s boyfriend Dean, who died in the fire. They learn that Amelia and Dean were working with Misty on an “experimental film” — combining pornography and investigative journalism — called How Do You Like My Car, Big Boy?
The two infiltrate a party in search of the film’s financier, Sid Shattuck. Healy discovers the film is missing, while a drunken March finds Shattuck dead, and unknowingly crosses paths with Amelia. March’s daughter Holly, having snuck along to the party, manages to stop Blueface from killing Amelia. Blueface is struck in a hit-and-run, and Amelia flees. Healy subdues Older Guy and finds Blueface dying, who tells Healy his boss has dispatched a hit man named John Boy to kill Amelia, March, and all other witnesses. Healy discreetly strangles Blueface to death. The police arrive at the scene, and March and Healy are met by Amelia’s mother, Judith Kuttner, a high-ranking official in the Justice Department , who claims Amelia is delusional and believes Judith wants her dead. Judith hires the duo to find her daughter.