California, 1970. Beach hippy and private eye Larry ‘Doc’ Sportello (Joaquin Phoenix) receives an unexpected visit from his ex-girlfriend Shasta (Katherine Waterston). She has been seeing wealthy, married property developer Micky Wolfmann (Eric Roberts), and suspects that his wife is plotting to have him kidnapped and committed to an insane asylum. Despite Doc’s lingering feelings for her, Shasta wants him to investigate the case.
It turns out that the next two cases Doc is asked to take on both have a connection to Wolfmann. In fact it seems that everyone he stumbles across – from saxophonist Coy Harlington (Owen Wilson) to brothel worker Jade (Hong Chau) to bull-headed police detective ‘Bigfoot’ Bjornsen (Josh Brolin) – is somehow tangled in the web of conspiracy. Cults, communists, street gangs, white supremacists, the FBI, an international heroin smuggling operation, politicians, pirates (possibly) and a syndicate of dentists are all involved. None of it really seems to make a lot of sense; but Doc, shambling from clue to clue in a dope-induced stupor, is quite used to that.