"Death on the Nile" is in almost every conceivable way a step down from Branagh's last outing with the character, to say nothing of the Peter Ustinov-led version from 1978 or the David Suchet television adaptation of Christie's novel from 2004. But it's not because Branagh and screenwriter Michael Green fail to depict the general gist of the source material, which remains largely intact down to the memorable twists at the center of its murder mystery. Instead, it's because of how much unnecessary elaboration and tedium they stitch around the periphery of the piece. 

For the unfamiliar, the story centers around Hercule Poirot (Branagh), the world-famous detective, taking a holiday aboard the S.S. Karnak in Egypt that ends up interrupted by a murder. He's surrounded by the usual coterie of socialites brimming with plausible motives for having committed said murder, so he must conduct interrogations, piece together clues, and unpack the claustrophobic melodrama so dense it threatens to sink the very ship they're all stuck on. This particular subgenre has a well-worn but reliable shape, so there's ample room to make adjustments among the principal players in an effort to put new spins on old frameworks.

To its credit, Green's new staging of Christie's mystery makes room for a more diverse presentation of the original suspects list. Romance novelist Salomie Otterbourne and her daughter Rosalie become a jazz musician (Sophie Okonedo) and her niece (Letitia Wright). Andrew Pennington becomes Andrew Katchadourian (Ali Fazal), who is still a close confidante of the deceased, albeit it no longer a white one. The ensemble doesn't work quite as well as the one Branagh assembled for "Orient Express," but Hammer is pretty well suited to play Simon Doyle, the dashing cad who marries heiress Linnet Ridgeway (Gal Gadot), with Jennifer Saunders and Dawn French bringing the brisk warmth of their comedy act to a cast sorely lacking in charm.

But it's the way this mystery is arranged and how many ornamental pieces surrounding it bog the picture down that holds "Death on the Nile" back. 

Firstly, Tom Bateman returns from "Orient Express" as Bouc, a friend of Poirot's who has far more importance to the plot here than in that prior film, which is strange enough as he isn't in the original book at all. A subplot involving Bouc and his mother Euphemia (Annette Bening) serves both as a detour from the main mystery at hand and as a needless bit of muddled continuity from how the last film ended, swapping out the suggestion that Poirot would be called to Egypt to solve a mystery with a convoluted new first act that sets Poirot closer to elements of the story that ought to predate his own involvement.

Secondly, echoing the way Poirot's memories of his lost wife intruded on the "Orient Express" proceedings, an ill-advised and inert romance between he and Okonedo's Salomie feels awkward and shoehorned in. It's clear that Green sought a way to strengthen some of the themes in the mystery, but attempts to do so here in a way that just feels ancillary. 

And finally, this is a movie that opens with a ten-minute black and white prologue following a young Poirot in WWI, showing him using his mental acuity in the trenches while also answering why his facial hair is so garish. 

Yes, this is a movie that feels we the audience need to know the origin of Poirot's mustache. But why?