• The surreal ending of Luca Guadagnino's "Queer" may stump some fans.
• The film is based on William S. Burroughs' incomplete novel of the same name.
• The surreal ending is partly based on Burrough's life.

Director Luca Guadagnino's new erotic drama, "Queer," attempts to provide an ending to the unfinished classic 20th-century William S. Boroughs novel of the same name.

"Queer" — Guadagnino's second movie of the year following the hyped tennis drama "Challengers," his highest-grossing film yet — is based on a semi-autobiographical novel that Burroughs started writing in the 1950s. He published it unfinished in 1985.

The film and book are based on Burroughs' experience living with a heroin addiction in Mexico City in the 1940s and 1950s.

"Queer" tells the story of two lovers trying to find a hallucinogenic drug.

Both the novel and movie adaptation of "Queer" follow two protagonists and have a similar plot.

The insecure William Lee (Daniel Craig) becomes infatuated with and tries to charm Eugene Allerton (Drew Starkey), a young expat whom he meets in Mexico City.

Allerton is based on Burroughs's real-life love interest, Adelbert Lewis Marker: their relationship ended in heartbreak for the writer.

Allerton is sexually curious but not wholly interested in Lee. They journey together through South America to find a drug called Yage (ayahuasca) in the hope it will give Lee telepathic powers.

They don't find Yage in the book, but the movie takes a different approach.

When Lee and Allerton reach Dr. Cotter (Lesley Manville), a Yage expert, they persuade her to let them try it, leading to hallucinogenic scenes where Lee and Allerton's body fuse together.

Critics have described these scenes as "trippy" and "body-horror-surreal."

The pair achieve telepathy after taking the drug, and Allerton tells Lee, "I'm not queer. I'm disembodied," making it clear that there is no future for their relationship.

Guadagnino told Variety in September he enlisted the help of Justin Kuritzkes, the screenwriter for "Challengers," to write the script for "Queer," including the ending.

"Justin can be more precise about this, but I remember that we said, 'What is unfinished, we want to try to finish,'" Guadagnino said. "And in doing that, we have to understand why it was unfinished and how Burroughs would have finished it."

Guadagnino said the pair also spoke to Oliver Harris, a leading expert on Burroughs' life and a professor of American literature at Keele University, UK.

According to the film's production notes, the phrase "I'm not queer. I'm disembodied" came from Burroughs' journals, and reflects his unease about identifying as gay.

The final section of the movie is based on the novel's epilogue

The final part of the film is set two years after the trip to the jungle, and shows Lee's return to Mexico City.

This is based on the novel's epilogue, where Lee searches for Allerton, discovers he has left Mexico City, and dreams about him.

Instead of a dream, the movie enters another hallucinogenic, surreal sequence, where Lee sees himself in a doll house. In the following scene, Lee and Allerton are in a room, and Allerton places a glass on his head.

Lee shoots at the glass with a gun, but hits Allerton's forehead instead. There is no blood, and Allerton soon disappears.

This scene may be based on Burroughs accidentally shooting and killing his wife Joan Vollmer while they lived in Mexico City, which he wrote about in the 1985 introduction to "Queer."

"I am forced to the appalling conclusion that I would never have become a writer but for Joan's death, and to a realization of the extent to which this event has motivated and formulated my writing," he wrote.

Per Burroughs' biography, he used a glass on her head as a target, in a similar fashion to the scene in "Queer," to prove he was good at shooting, but hit her forehead. Burroughs was convicted of murder and given a two-year suspended sentence.

The film's final scene shows Lee back at his apartment, old and dying. Lee imagines Allerton appearing in his bed, draping a leg over his.

Guadagnino told Entertainment Weekly that this scene is meant to show Lee's lasting and "profound" connection with Allerton.

He said: "The task that we gave ourselves was always to make this a very romantic movie and a testament to this romanticism between Lee and Allerton, no matter how much they are in sync or not throughout this story of their encounter."