Meet the cast of Dark Angel
Viewers will see another side to Downton Abbey's Joanne Froggatt as she plays the murderous Mary Ann Cotton
Emma Fielding (Helen Robinson)
Who does she play? Helen Robinson is James' sister, who has been looking after the children.
Where have I seen her? Although Emma Fielding is mainly known for her stage work, she has also appeared in dramas including Cranfield, Arthur & George, and – like Morgan – The Suspicions of Mr Whicher.
Penny Layden (Margaret Stott)
Who does she play? Layden plays Mary Ann's mother and George's wife Margaret. When she becomes sick, Mary Ann is called home to nurse her – and, funnily enough, her health takes a turn for the worse.
Where have I seen her? Television credits include Call the Midwife, Silent Witness and EastEnders, but you might also have seen her on stage at the Old Vic or National Theatre.
