Although Nigel believes he can identify the poison pen writer at an early stage, tensions and dangers escalate when Celandine is presented with a pair of binoculars rigged to shoot needles out of the eyepiece when the focus is adjusted. The Blicks have access to a machine workshop, but so does Durdle, and it's possible that the cruel gift was the result of a conspiracy. When the secret relationship between Charles and Rosebay becomes known, Sir Archibald – a fervent proponent of eugenics – flies into a rage and threatens to cut his son out of the family legacy. His objections are short-lived, literally: the next morning he is found dead at the bottom of a quarry.
The Dreadful Hollow finds Nicholas Blake poised perfectly between the puzzle plotting of his earliest books – plotting at which he excels far beyond the average mystery fiction author, by the way – and the brooding character psychology that will consume some of his later titles (see 1961's The Worm of Death, for example). But here, the twin interests are given the liberty to complement each other, and it is a mostly successful blending of classic detection and the character-based psychoanalysis that will largely replace it as crime literature moves through the 20th century.
I have always admired Blake's fair-play clue crafting, and it is still evident here. He refuses to condescend to the reader, and often I found myself making a deductive connection only to have Nigel Strangeways voice the same idea before extrapolating past it and continuing to connect the dots. Where a lesser writer may have left a clue observed but unexplained until the denouement, Blake underlines it and works out the possibilities on the spot.
One example: a row of crushed wildflowers near the quarry means a) that Celandine's electric wheelchair was here recently, and b) it might not have been manned by Celandine, since she is a lover of nature and would not drive over the flowers if she could help it. But then Nigel continues to hypothesize: c) the track is not deep enough if the wheelchair carried the weight of two bodies, Celandine's and Archibald Blick's; d) the chair's motor was drained the day of the murder, so Celandine could not use it to drive up to the quarry and back with a dead or unconscious Sir Archibald, et cetera. It is quite enjoyable to play Watson while the detective is doing some real-time theorizing; many mystery writers let their creations sit on their hypotheses until it's time for the drawing room reveal, but this has never been the case with Blake and Strangeways, and that's to be commended.