It's 1857 and 24-year-old Mary Ann Cotton has come home to Seaham, County Durham after four years away, having eloped to Cornwall with Billy Mowbray. Her mother, Margaret, and kindly step father George Stott, welcome them with open arms.

The two-part drama, Dark Angel, from Line of Duty makers World Productions, is based on the extraordinary true story of the Victorian poisoner Mary Ann Cotton. Travelling around the North-east, she insinuates herself into unsuspecting families, marrying and creating new families of her own - before killing them, taking their money and moving on.