Visiting Bellfield Hall to comfort her niece, who has been seemingly abandoned by her wealthy fiancé, Miss Dido Kent investigates the possibly related death of a young woman, a situation that is complicated by surprising secrets.

On a visit to the ruins of Madderstone Abbey, Penelope Lambe suffers a bad fall from the ancient stone steps. Before she slips into unconsciousness, Penelope manages to say, 'I saw her - It was her.' The Crockford sisters are sure that what made Penelope fall was that she saw the Grey Nun, the ghost that is reputed to walk the abbey's ruins.