Dark Angel

With her wide-eyed innocence, Joanne Froggatt is the last person you’d suspect of murder, which made the unjust accusation of that crime against anna bates, the maid she played in Downton Abbey, all the more affecting.

Now, in a coup of reverse casting, she stars in Dark Angel (ITV, Monday, 9pm) as Mary Ann Cotton, whose penchant for liberally distributing arsenic left a trail of bodies across the north- east of Victorian England. Cotton holds some unenviable records: married three times, widowed three times, plus a common-law husband who followed her other men to an early grave – and out of 13 children, just two survived. The motive was simple: life insurance payouts. (Yes, men, pay attention the next time your loved one brings up the subject of your policy.)

From the start of this two-part series, we know exactly where the tale is going, thanks to a sobering glimpse of the gallows, to which this black widow is surely headed. Dramatically, the question is how can the Angelic Froggatt be transformed from the saint who served the Granthams into a prolific serial killer who’ll stop at nothing for her own gain?