American Ursula Grandison accompanies Belle Seldon to visit her sister, Helen, Countess of Mountstanton, commissioned by their father, multi-millionaire Chauncey Seldon, to discover what is wrong with Helen's marriage and what has happened to her dowry. At decaying stately Mountstanton House, Ursula finds the Earl is a cold fish, the Dowager Countess of Mounstanton the mother-in-law from hell, and Helen has not forgiven her for stealing her great love. Ursula discovers the drowned body of Polly, the nursemaid, thought to have deserted the household. Neither the Earl's brother, Colonel Charles Stanhope, nor Ursula believes Polly's death was an accident. Investigating against the Earl's wishes, they uncover a tangle of deception reaching into the past that threatens the reputation of the house of Mountstanton. After another death, Ursula fights to reveal the truth, to save Belle from dreadful scandal, and to fulfil Mr Seldon's commission, with a final shocking denouement.