This seems to be another of the forgotten Penguins. Online references only lead to copies listed for sale, and there is very little information available concerning the author. I could find only that John Ferguson was a Scottish clergyman who wrote ten detective novels, although he was better known as a playwright. This is one of six which feature the Scottish private detective Francis McNab, and one of four published as numbered Penguins.
The plot is complex, with the story written more as a thriller than as a conventional crime novel. We know many of the details of the crime from the early chapters, and although clues are scattered throughout, they are not there to help the reader solve a puzzle; this is the story of a pursuit. The question being considered is how you would track down an otherwise respectable man who committed a single murder. England in 1928 was filled with young men trained to kill during the war, but what if they used their training once, and only once, in civilian life? The suggestion is that the police would never find them, for they lack training in logic. They draw predictable inferences from all they observe, fail to consider competing hypotheses, and willingly ignore any clues at odds with their conjectures. Francis McNab has been trained in logic. He is hired to investigate the murder by a newspaper with an eye on its circulation.
Sandy Kinloch is the man in the dark. He was left blind as the result of an explosion in the First World War, and he is destitute. He had once been a medical student with an inclination for literature and a promising future, but ill-fortune together with the war, his injuries, and some poor investments, have reduced him to penury. He spends his last few borrowed coins to travel to Ealing on a fog-bound London night to beg some help from a former fellow student, Dr Peter Dunn.
But Kinloch and Dunn are Scottish, and they seem to share with the other Scottish characters in the book a set of personality traits which makes it difficult for them to get along with others: they are proud, sensitive, and quick to take offence, and they treat conversation as though it were some type of fencing match, always looking for opportunities to wound each other. Kinloch leaves Dunn's house angry, penniless, and without options, and inadvertently stumbles into the path of Ponsonby Paget, whose murder later that evening will alter the course of his life.
Paget is a politician and journalist, strangely esteemed by the general public for his weekly newspaper, the Eye Opener, a publication devoted to exposing the private lives and secrets of London's well known citizens. He is kept in business by a steady stream of women (and only women) willing to sell him gossip for publication. But gossip can be put to other uses, and people will pay to have a story disappear. Paget's miscalculation was to blackmail someone who was also willing to kill. Kinloch is a witness to all that occurs, lured from the fog in his desperate state by the promise of earning an easy five pounds. But he is a witness in no position to identify the murderer, and he is likely to be a suspect himself.
It is clear that the murderer will only be identified if Kinloch can be traced, but Kinloch has reasons for remaining elusive. The police have no chance of finding him: they have inferred from the crime scene that Kinloch is lame rather than blind, and they have embarked on a futile search. The story evolves as a three-tiered game of hare-and-hounds: Kinloch on the trail of the murderer, and McNab on the trail of the blind man. It is completely unbelievable, and yet engagingly written, told partly in the present and partly in retrospect, using three narrators who have differing perspectives and differing loyalties.
It has those staples of the genre, the dim offsider who must have every aspect of the solution explained, and the scoffing at crime fiction generally, with the suggestion that in a fictional world all the clues would be more apparent and more easily deciphered. And yet many of the clues presented here are absurdly fortuitous; only the slightest deviation and the crime would have remained unsolvable. However, it was well written, interestingly structured, and enjoyable to read.