Spoiler alert! The following post contains details about the ending of “A Haunting in Venice.”

Hercule Poirot is back on the case.

Agatha Christie’s most famous creation is probing yet another mystery in “A Haunting in Venice” (now in theaters), the third in a series of Christie adaptations directed by Kenneth Branagh, after “Death on the Nile” (2022) and “Murder on the Orient Express” (2017).

The supernatural whodunit is loosely based on Christie’s 1969 detective novel “Hallowe’en Party,” and features a star-studded cast including Tina Fey, Jamie Dornan, Michelle Yeoh and Kelly Reilly. Here’s how the book and film compare:

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What’s changed between ‘A Haunting in Venice’ movie and book?

Unlike Branagh’s other Christie adaptations, which closely follow their source material, “A Haunting in Venice” is an almost entirely different story than “Hallowe’en Party.” In the book, the mustachioed Poirot is summoned to a sprawling English estate, the site of several murders. At a Halloween party one evening, a 13-year-old girl claims to have witnessed one of the killings, and hours later, she is found dead in an apple-bobbing tub.

The spooky bash is one of the only similarities between the book and movie. In “A Haunting in Venice,” Poirot (Branagh) is called to a Halloween party at the Italian manor of Rowena Drake (Reilly). He’s invited there to help disprove the work of Joyce Reynolds (Yeoh), a medium conducting a séance for Drake’s daughter, Alicia, who plunged to her death from a balcony.

With this film, Branagh and screenwriter Michael Green wanted to dip their toes into the horror genre.

“We had done two very faithful adaptations of two pretty famous, pretty big books,” executive producer James Pritchard told entertainment site The Direct. “(We) felt that we should maybe surprise our audience with this and try something a little bit different."

Are Michelle Yeoh and Tina Fey's characters in the 'Hallowe'en Party' novel?

Coming off her Oscar win for “Everything Everywhere All at Once,” Yeoh is naturally front and center in all the marketing for “A Haunting in Venice.” So it may come as a shock that Yeoh only has a few minutes of screen time and – spoiler alert – is the first one murdered in the movie, after she’s pushed from a ledge and impaled on a statue.

Although there is no medium or séance in “Hallowe’en Party,” Yeoh’s new character has literary roots: Joyce Reynolds is the name of the teenage girl killed at the start of the novel.

Along with Poirot, Fey’s character also appears in the book. The “30 Rock” actress plays Ariadne Oliver, a crime-fiction writer and one of Poirot’s friends. Ariadne is featured in more than half a dozen Christie novels and short stories, including “Mrs. McGinty’s Dead” (1952) and “Dead Man’s Folly” (1956).

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'Haunting in Venice' ending, explained

Rowena is one of two murderers in “Party,” but in “Venice” she is the big bad. At the end of the film, we learn that Rowena had slowly poisoned Alicia to keep her feeble and childlike and prevent her daughter from leaving home and getting married. But when a housekeeper mistakenly gave Alicia an overdose, Rowena tried to frame it as a suicide by throwing her daughter's body off a balcony. Later, Rowena killed Joyce and party guest Dr. Leslie Ferrier (Dornan) for seemingly knowing too much about Alicia's death.

In a climactic standoff with Poirot, Rowena meets a watery grave when she is pulled into the Venice canals by Alicia’s spirit. Although he has long favored science over superstition, it’s enough to make Poirot start believing in ghost stories.