Educated Emily (Lydia Wilson) is working as a lady's companion for Lady Maria (Joanna Lumley) when she receives a marriage proposal from her employer's widowed nephew Lord James Walderhurst (Linus Roache). Later, when Lord James departs to rejoin his regiment, Emily is left to bide her time in a secluded country estate with her husband's nephew Alec Osborne (James D'Arcy) and his elegant wife Hester (Hesina Haque). Later, as the Osborne's begin to reveal their dark side, Emily begins to fear that she won't live long enough to be reunited with her husband.