Comings and goings at Downton Abbey Maggie Smith and Shirley MacLaine in Downton Abbey season three. SPOILER ALERT: Shirley MacLaine will be returning to Downton Abbey, as opera star Kiri Te Kanawa joins the cast. Carnival Films and Masterpiece on PBS say MacLaine will be reprising her role as Martha Levinson, Lord Robert Crawley's freewheeling American mother-in-law. There are few details on Dame Kiri's role but it is believed that the world-renowned soprano will sing. Meanwhile, the producers are confirming that villainous housemaid Sarah O'Brien won't be back. Siobhan Finneran, who played her, is leaving the series. These announcements on Saturday follow the third season's recent airing in the United States. It concluded last month with the death of popular character Matthew Crawley, thanks to departing cast member Dan Stevens. Lady Sybil Branson also died. She was played by the exiting Jessica Brown Findlay.