Dark Angel, ITV

Having served her time as dutiful, self-effacing Anna Bates in Downton Abbey, here's Joanne Froggatt grasping with both hands the role of Mary Ann Cotton, "Britain's first female serial killer". No more wearing herself out desperately trying to save Mr Bates from the gallows. This time she's turning the tables, and making sure useless men aren't going to hold her back any longer.  

After a short prologue in which our anti-heroine was preparing to meet her maker, we joined her as she returned to her mother and stepfather's pub in Seaham, County Durham in 1857. She had eloped to Cornwall four years earlier, married Billy Mowbray (Tom Varey, pictured below) and borne five children, four of whom had died. Her children would keep expiring at dismally frequent intervals, though it wasn't clear how many of these cases were by Mary's hand or from natural causes (the real-life Mary Ann may have dispatched as many as 21 victims).

Being married to her was also likely to prove injurious to a fellow's long-term prospects, as Billy discovered after she wearied of him being away at sea for most of the time. He was followed by the unfortunate George Ward (Thomas Howes), whom she met when he was a patient in the hospital where she worked for a time as a nurse, and then there was... but that would be rushing ahead prematurely to next week's concluding episode.

No judge or jury was ever likely to buy the idea of mitigating circumstances for Mary Ann's appalling crimes, but Dark Angel effectively conveys the miserable lot of the working poor in Victorian England (and of course they weren't just pretending, unlike the poverty-tourists in BBC One's The Victorian Slum).  "It's just how life is for women," opined Mary Ann's mother, after child number six – or was it seven? – had died, ostensibly of scarlet fever. When Billy decided they had to move to Sunderland so he could find work at the docks, Mary Ann found herself confined to the bedsit from hell, frantically trying to scour layers of filth from the floorboards while dodging the wildlife hopping about in the bedclothes. Her husband's poor pay and interminable absences meant she was constantly scrabbling around for money to pay the bills.

It was enough to make a woman turn to... well tea, actually. However, we soon learned that rather than being the cup that cheers (but does not inebriate), Mary's special brew was a short cut to the morgue. Her additive of choice was arsenic, whose symptoms of vomiting and diarrhoea were almost certain to be interpreted by a harassed local doctor as some sort of gastro-intestinal illness rather than murder most cynical. Not even Mary Ann's poor, sick old mum (Penny Layden, pictured above with Froggatt and murderous teapot) got the benefit of the doubt. "There's a darkness in you, Mary Ann", she lamented, having discerned that her daughter had been shagging the sleazy ne'er-do-well Joe (Jonas Armstrong) under the pier. "Let me make you a nice cup of tea," said Mary Ann, with a smile that could have turned anti-freeze into an iceberg.

Grim as all this was, Froggatt's performance is a marvel of meticulously observed nuances. Judging by contemporary photographs, the real Mary Ann more closely resembled Mr Bates than his wife, but Froggatt can spin nimbly from grey-faced exhaustion or tearful misery to full-beam seductiveness, despite being encumbered with the full kit of skirts, bloomers and bonnets. The moment when she led her latest target, the bereaved and vulnerable James Robinson (Sam Hoare), up his staircase by turning to fix him with a gaze both demure yet lascivious was extraordinary. Gong-style recognition may be her reward. 

• Read more TV reviews on theartsdesk