Downton Abbey standout Joanne Froggatt is to star in Dark Angel, a small-screen, two-part drama, which is based on the true story of the Victorian-era poisoner Mary Ann Cotton, ITV announced.

The British broadcaster's director of drama, Steve November, and controller of drama, Victoria Fea, have commissioned the miniseries.

"Dark Angel is an extraordinary and chilling true story," Fea said in a statement. "We're delighted to have an actress of Joanne Froggatt's caliber in the lead role. 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."

Dark Angel was written by Gwyneth Hughes and will be directed by Brian Percival. It is inspired by the book Mary Ann Cotton: Britain's First Female Serial Killer by David Wilson.

Downton Abbey will begin airing episodes in its sixth and final season later this year.