Andrea Riseborough has signed on to play the role of Romaine in the BBC’s adaptation of Agatha Christie’s The Witness for the Prosecution. The two-parter will be a Christmas special for the broadcaster. Penned by Sarah Phelps, a longtime writer on popular soap Eastenders, the story is based on one of Agatha Christie’s better known short stories. Leonard Vole is arrested for the murder of Emily French, a wealthy older woman who was unaware that he was involved with another woman, Romaine. Emily made Leonard her principle heir, casting suspicion on him. John Mayhew, lawyer, down on his luck – comes to his rescue when Romaine agrees to testify not in his defense but as a witness for the prosecution.