The Replacement

As this gripping three-part thriller begins, Ellen (Morven Christie, above right) seems to be sailing on the crest of life’s wave. An architect, she works at the world’s nicest business, for the world’s nicest bosses, who also happen to be her best friends; her adoring husband is a psychiatrist, able to spot any signs that the ghosts of Ellen’s past may be returning to haunt her. When Ellen becomes pregnant she hires Paula (Vicky McClure, above left) to cover her maternity leave. But Paula soon causes Ellen’s hackles to rise – she’s too competent, too keen, too familiar – and Ellen’s loved ones start to fear that the pregnancy is adversely affecting her mental health. Is Ellen paranoid, or is Paula really trying to oust her? Tuesday, 9pm, BBC1.