PICK OF THE DAY

THE REPLACEMENT, 9PM, BBC1

AS THIS gripping three-part thriller begins, Ellen (Morven Christie) is on the crest of life’s wave. An architect, she works at the world’s nicest business, for the world’s nicest bosses, who 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, pictured near right with Christie) 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 fear that the pregnancy is affecting her mental health. Is Ellen paranoid or is Paula really trying to oust her?