They don’t make ’em like this anymore: an old-school murder mystery, based on the 1969 novel “Hallowe’en Party” by the maestra of the genre, Agatha Christie, and featuring a stellar cast, including Michelle Yeoh, Tina Fey, Jamie Dornan, Camille Cottin and Kenneth Branagh. Well, Branagh still makes ’em like this. Set in post-World War II Venice, this is the director’s third Christie adaptation, after “Murder on the Orient Express” in 2017 and last year’s “Death on the Nile.” Once again, Branagh plays Christie’s famous Belgian detective, Hercule Poirot, all extravagant mustache and Sherlockian powers of deduction, who comes out of retirement to solve the murder of a guest at a seance he’s reluctantly attending. In an age of Knives Out mysteries and “See How They Run,” which cheekily tweak the conventions of the genre, Branagh’s films are sterling examples of an increasingly obsolete form of straight-faced whodunit. The director hasn’t said whether he’ll make more, but he has plenty of material: Poirot appears in 33 novels by Christie, as well as two plays and 51 short stories.