See Joanne Froggatt as a serial killer in new role

Froggatt’s character sounds like the complete opposite to Downton’s dependable maid Anna Bates, as she has a secret history of adultery, bigamy, fraud and murder.

Froggatt will return for the final series of Downton Abbey next month, which will conclude with its Christmas special on Christmas Day. Filming is happening in North Yorkshire & County Durham.

The Downton Abbey star has signed up to appear in two-part ITV drama Dark Angel about the real life murderess.

The gripping story will tell of how Cotton, who was originally from Houghton-le-Spring, set about poisoning her victims with arsenic over an eight-year period in an apparent attempt to benefit from insurance money. But faced with abject poverty and an ailing husband, we see how ruthlessly determined she is to pursue her desires – and a better life …

“Dark Angel is an extraordinary and chilling true story”, said ITV’s Controller of Drama Victoria Fea, who commissioned the two-parter alongside Director of Drama Steve November.

Travelling all over the North East, Mary Ann immerses herself into the bosom of unsuspecting families, marrying and creating families of her own – before murdering them, taking their cash, and them moving on to the next victim. They say the drama introduces Cotton as a loving wife and mother, newly returned to her native North-East.

“The combination of a tautly written script, an outstanding cast and great producers in World Productions make this a really exciting addition to the ITV drama slate”.