Color me impressed with Nicholas Blake because I loved this book. Nicholas Blake was a pseudonym for Cecil Day Lewis, father of Daniel Day Lewis and Poet Laureate of the UK from 1968 until 1972. This must explain his facility with words and language, as well as his familiarity with Elizabethan tragedy.
The plot is classic Golden Age - the victim, Fergus O'Brien, dashing pilot and war hero, contacts our intrepid amateur sleuth, Nigel Strangeways, because he has been receiving threatening letters. He engages Nigel to come to a house party he has planned at the Dower House, which he rents from Nigel's aunt & uncle. Everyone he can remotely conceive as having a motive to murder him has been invited to the house party because why not?
The book takes a bit to get going, and then Fergus turns up dead, just as the letter writer had threatened. As Nigel tries to work out the puzzle, there are a couple of additional deaths to complicate matters. Fergus's murder itself is a classic "impossible crime," although the solution to this element is fairly pedestrian. It's not, as the local Inspector claims early in the book "soopernatural."
Nigel is able to work the whole thing with some cleverness and a quick trip to Ireland. There is also a heart-pounding air pursuit when the chief suspect flees from Dower House and tries to escape by air to France or Spain. At the end, Nigel reveals all to his uncle, the and an old professor who had also been one of the guests in classic Golden Age fashion, with an explanation over sherry in Nigel's town flat.
Thou Shell of Death is the second outing for Nigel Strangeways, who appeared first in A Question of Proof, which is set in a boy's school. The fourth book, The Beast Must Die, is one of the featured books for Chapter 24 of TSoCC. Most of them are available through the Kindle Unlimited library, for anyone who subscribes.