Former NBC "ER" actress Alex Kingston will be joining the cast of the BBC's drama "Upstairs Downstairs." The 48-year-old actress will play the character Blanche Mottershead, the younger sister of Dame Eileen Atkins's character Lady Holland when the show returns next year, the BBC said Sunday. "I simply couldn't resist the opportunity to get inside the iconic 165 Eaton Place," said Kingston. Kingston's casting follows Atkins's announcement that she will not be returning for the next season. The new season will begin production in October and will be set in 1938, spanning the months leading up to the start of World War II. "Outside 165 Eaton Place, London and Europe are poised on the knife-edge of calamity," said show writer Heidi Thomas. "Inside, there's a whole world of dark and dangerous emotions to explore." "Heidi really has created a wonderfully, intriguing character in Blanche who will over time reveal some secrets of her own," said Kingston. Actor Kenneth Cranham will also be joining the cast of the show, which follows the lives of the masters and servants who live in a London townhouse.