The film opens during the recording of Jim's An American Prayer and quickly moves to a childhood memory of his family driving along a desert highway in 1949, where a young Jim sees an elderly Native American dying by the roadside. In 1965, Jim arrives in California and is assimilated into the Venice Beach culture. During his film school days studying at UCLA, he meets his future girlfriend Pamela Courson, and has his first encounters with Ray Manzarek, as well as the rest of the people who would go on to form the Doors, Robby Krieger and John Densmore.
Jim convinces his bandmates to travel to Death Valley and experience the effects of psychedelic drugs. Returning to Los Angeles, they play several shows at the famous nightclub Whisky a Go Go and develop a rabid fan base. Jim's onstage antics and occasionally improvised lyrics raise the ire of club owners; however, the band's popularity continues to expand.
As the Doors become hugely successful, Jim becomes increasingly infatuated with his own image as "The Lizard King" and degenerates into alcoholism and drugs. Jim meets Patricia Kennealy, a rock journalist involved in witchcraft, and participates with her in mystical ceremonies. He joins her in a handfasting ceremony. An elder spirit watches these events.
The rest of the band grows weary of Jim's missed recording sessions and absences at concerts. Jim arrives late to a Miami, Florida concert, becoming increasingly confrontational towards the audience and allegedly exposing himself onstage. The incident is a low point for the band, resulting in criminal charges against Jim, cancellations of shows, breakdowns in Jim's personal relationships, and resentment from the other band members.
In 1970 after a lengthy trial, Jim is found guilty of indecent exposure and ordered to serve time in prison, he is however allowed to remain free on bail pending the results of an appeal. Patricia tells Jim that she is pregnant with his child but Jim convinces her to have an abortion. Jim visits his fellow Doors members one final time, attending a party thrown by Ray where he wishes the band luck in their future endeavors and gives them all a copy of An American Prayer. As Jim plays in the front garden with the children, he sees that one of the children is his childhood self. Jim comments "This is the strangest life I've ever known."
In 1971, Pam finds Jim dead in a bathtub in Paris, France, at the age of 27. Pam dies three years later of a drug overdose, also at the age of 27.
The final scenes of the film before the credits roll are of Jim's gravesite in PĂ¨re Lachaise Cemetery in Paris while "A Feast of Friends" plays in the background. Just before the credits, the screen whites out and text appears saying "Jim Morrison is said to have died of heart failure. He was 27. Pam joined him three years later."
During the credits, the band is shown recording the song "L.A. Woman" in the studio.

Question: What was the alleged cause of Jim's death?
Answer: His death was attributed to heart failure.
Alternative answer: Heart failure.