A sun-soaked tale full of beautiful rich people doing terrible things, including a transgressive sexual act that’s got the tabloids foaming at the mouth. On paper, BritBox import “Towards Zero” sounds like another salacious drama to ride on the coattails of “The White Lotus.” Yet it stems, in fact, from the bygone era of cozy crime fiction where the only stiff appendage was the upper lip.

Indeed, following the likes of “And Then There Were None,” “The Pale Horse,” and “Ordeal by Innocence,” the 1930s tale is the latest Agatha Christie whodunit to get a semi-contemporary spin. And just like her predecessor, period drama queen Sarah Phelps, screenwriter Rachel Bennette gives the purists plenty to scream blue murder over.

“BBC viewers left stunned by ‘filthy’ X-rated scene,” was a typical conservative media headline after the three-part series premiered in the UK last month. “Is ‘Towards Zero’ the raciest Agatha Christie ever?...