Not "The Witcher". This is on 'zon, "The Murder at Roadhill House", there are 3 more episodes so far. Based on a 2008 book by Kate Summerscale.
Period 1860, in a crappy English village of Wiltshire, a family awakes to find a missing child (called a "baby" and kept in a crib, but he's nearly 4), and when he's found dead, early Scotland Yard is called, they send a sad-faced Paddy Considine as the improbably-named but historically real Mr Whicher, though the actor doesn't fit the character well:
Whicher was reportedly described by a colleague as the "prince of detectives". Charles Dickens, who met him, described him as "shorter and thicker-set" than his fellow officers, marked with smallpox scars and possessed of "a reserved and thoughtful air, as if he were engaged in deep arithmetical calculations". William Henry Wills, Dickens's deputy editor at Household Words magazine, saw Whicher involved in police work in 1850 and described him as a "man of mystery".
The start's very slow, and often uses voice-over repetition to pad out scenes that would just be Paddy walking around looking at things. Later in the first ep, they send along a sergeant, "Dolly" (William Beck), which helps with dialogue, though he gets vanishingly little character development. The local authorities are unhelpful, hostile, closed-minded fools you'd expect of the still-medieval backwater English.
Whicher's not quite a modern, scientific detective, but he tries. And he's a bit moody, especially between cases he's as useless and dissolute as Sherlock Holmes; which is probably a modern back-adaptation from Arthur Conan Doyle's 1880s books.
The pacing is glacial, much plot happens off-camera, and an early version of spinning-newspaper headlines. Very little time is spent on backstory outside of the main suspects; I wonder if the book goes deeper, or if this is all there is.
Still, it's a good enough mystery, Whicher's worth watching, what-cha.