In Gladys Mitchell's latest book the scene throughout the story is a Norman castle in the courtyard of which a small manor house has been built.

Under pressure from a small boy who wants to spend his summer holiday there, Dame Beatrice Lestrange Bradley is persuaded to rent the estate, only to find that an unexplained violent death occurred there some two years previously and that the murderer has never been found. The police have a suspicion that they know his identity, but there is no proof.

The dead man was Thomas Dysey, a previous owner of the estate, but it is so impoverished that there seems no reason for supposing that the murder was committed by one of his relatives for gain, although, in the absence of all other conceivable motives, there seems no other cause for his death.

It turns out that he has an illegitimate son named Henry and a legitimate son, Bonamy. The former is debarred by his illegitimacy from inheriting, and the latter who got into disgrace in England, is said to have died abroad. This leaves Thomas Dysey's wife and his twin brothers, one of whom has adopted the illegitimate son, and these have become the main suspects. During the early part of Dame Beatrice's tenancy, the castle appears to be haunted by a singing ghost, but his spectral nature is soon in doubt, as, twice a week, on Wednesday nights and Sundays, he steals food from the manor house pantry. The situation is further complicated by the fact that on Wednesdays and Saturdays the house and castle are thrown open to the customary half-crown visitors, one of whom may be the murderer.

The singing ghost appears to be exorcised when one of the dead man's twin brothers is also murdered, and in precisely the same way. This presupposes that the murders are dynastic and that possession of the almost worthless property is the murderer's ultimate aim. This is the police theory.

There is also a strong local rumour that the manor house once sheltered Jesuit priests during the time when the Catholic faith was proscribed, and that these left behind a treasure known as the Dysey Hoard. Nobody seems to know whether the treasure is still in existence or, if so, what form it takes, and Dame Beatrice tries to trace its history in the hope that this will shed some light on the two murders.

Two other possible suspects exist in the form of a woman whom one of the brothers has married, and her sister, who is Henry's mother, but although these women could have murdered Thomas as an act of revenge for begetting Henry, there seems no reason why they should have killed the second brother. All appears to turn upon whether the legitimate son, Bonamy, is alive or dead. When he turns up, not only alive but married with a son of his own, the mystery of the two murders seems insoluble until Dame Beatrice tracks down the truth.