You can always count on Agatha Christie for a surprise, and the big twist in A Haunting in Venice is that it's actually a pretty terrific movie.

I say this as a die-hard Christie fan who didn't much care for Kenneth Branagh's earlier adaptations of Murder on the Orient Express and Death on the Nile. Charming as he was in the role of Hercule Poirot, the movies themselves felt like lavish but superfluous retreads of two of the author's best-known classics.

One of the lessons of A Haunting in Venice is that sometimes, it's a good idea to go with weaker source material. Christie's 1969 novel Hallowe'en Party is one of her thinner whodunits, and Branagh and his screenwriter, Michael Green, have smartly overhauled the story, which is now set in 1947 Venice. They've also gleefully embraced the Halloween theme, taking the cozy conventions of the detective story and pushing them in the direction of a full-blown haunted-house thriller.

OK, so the result isn't exactly Don't Look Now, the most richly atmospheric horror movie ever shot in Venice. But Branagh and his collaborators, especially the cinematographer Haris Zambarloukos and the production designer John Paul Kelly, have clearly fallen under the spell of one of the world's most beautiful and cinematically striking cities. While there are the expectedly scenic shots of gondolas and canals at sunset, most of the action takes place after dark at a magnificent palazzo owned by a famed opera singer, played by Kelly Reilly.

She's hosting a lavish Halloween party, where Poirot is one of the guests, tagging along with his longtime American friend, Ariadne Oliver, a popular mystery novelist played with snappy wit by Tina Fey. Also in attendance are Jamie Dornan as a troubled doctor and an entrancing Michelle Yeoh as a medium, known as "the unholy Mrs. Reynolds," who says she can speak to the dead.

Mrs. Reynolds performs a séance, hoping to contact the spirit of the opera singer's daughter, who died under mysterious circumstances at the palazzo a year earlier. Soon another death will take place: One of the party guests turns up murdered, and while Poirot is officially retired, he decides to take on the case. He even asks his mystery-writer friend, Miss Oliver, to help him interview suspects, though not before first questioning her about her whereabouts at the time of the killing.

As Poirot, Branagh is clearly having so much fun wearing that enormous mustache and speaking in that droll French accent that it's been hard not to enjoy his company, even when the movies have been lackluster. For once, though, the case he's investigating is just as pleasurable to get lost in.

It's an unusually spooky story: The palazzo, we find out early on, is rumored to be haunted by the vengeful ghosts of children who died there years ago during an outbreak of the plague. Branagh piles on the freaky visuals and jolting sound effects, to the point where even a supreme skeptic like Poirot begins to question what's going on. These horror elements may be unabashedly creaky and derivative, but they work because the movie embraces them to the hilt.

A Haunting in Venice sometimes feels closer to the work of Christie's undersung contemporary John Dickson Carr, whose brilliant detective stories often flirted with the possibility of the supernatural. That said, the actual solution to the mystery, while clever enough, isn't especially ingenious or complicated.

What gives the story its deeper resonance is its potent sense of time and place. It's just two years after the end of World War II, and many of the suspects have witnessed unspeakable horrors. The medium, Mrs. Reynolds, was a nurse during the war, which may account for why she feels such an affinity for the dead. Everyone, from the grieving opera singer to the doctor traumatized by his memories, seems to be mourning some kind of loss.

In Branagh's retelling, Poirot is himself a World War I veteran. One of the reasons he's such a staunch atheist is that he's seen too much cruelty and suffering to believe that God exists. He doesn't exactly change his mind by the end of A Haunting in Venice. But it's a testament to this movie's poignancy that Poirot emerges from his retirement with a renewed belief that he can still do some good in the world. He's eagerly looking forward to his next case, and so, to my delight, am I.