It's 1941, and the Mitford household is splintered by the vicissitudes of war. To bring the clan together - maybe for one last time - Deborah invites them to Chatsworth for Christmas, along with a selection of society's most impressive and glamorous guests, as well as old family friend Louisa Cannon, a private detective. One night, a psychic arrives, and to liven things up Deborah agrees she may host a séance. But entertainment turns to dark mystery as the psychic reveals that a maid was murdered in this very same house - and she can prove it. Louisa steps forward to try to solve the cold case. But with a house full of people who want nothing more than to bury their secrets, will she be able to unmask the murderer? And how deep does the truth lie?