While going through his late brother's effects some months after his murder, Gerald Heatherdale finds a typewritten note warning Austin to stay away from Horn's Lane - the isolated copse near his country house where his body was found. Gerald carries the note to Dr Lancelot Priestley, hoping that the scientific detective will be able to shed new light on the unsolved crime. Questioned, Gerald admits that he was his brother's main heir, but further explains that under their father's will, the two of them were bound with a Captain Murchison to the upkeep and operation of a cargo-ship, the financial obligation to fall upon the survivors should any of the three die. Although he finds Gerald's account of the circumstances of the murder suggestive, Dr Priestley can offer no better advice than for the note to be taken to the police. However, the situation takes a new and startling turn when Priestley and his secretary, Harold Merefield, are abruptly summoned by Gerald and learn that he has received an identical warning to stay away from Hilton Pennings - a lonely copse near his Wiltshire cottage. Priestley and Merefield arrive to find Gerald in a state of nervous collapse, and persuade him to return to London with them. Such is Gerald's terror that Priestley decides it would be best if he left England altogether, and arranges with Captain Murchison to take him on his ship's next voyage. But when the ship embarks, it is without Gerald - whose body is later found in a ditch in Hilton Pennings...

Dr Priestley's Quest is the second entry in John Rhode's extraordinarily long-running series about Dr Lancelot Priestley, a Professor of Mathematics who occasionally dabbles in crime investigation out of a passion for facts. The first book in the series, The Paddington Mystery, is today practically unobtainable and a prime collector's item; so we are left to make inferences about it from this second work. Dr Priestley's Quest is narrated by Harold Merefield, the fiancé of Priestley's daughter, April, and the beneficiary of Priestley's analytical skills after being falsely accused of a crime. Subsequently, Merefield was employed by Priestley as his secretary, and also functions as his "Watson" on those occasions when the professor's interest is caught by a particular mystery.

Although hugely popular in its day - indeed, Dr Priestley eventually superseded Dr John Thorndyke as England's pre-eminent "scientific detective" - the series as a whole was notoriously condemned by leading critic Julian Symons as "of the hum-drum school", and on the basis of Dr Priestley's Quest, I'm inclined to agree. The book is satisfactory as a puzzle, but distinctly lacking on the level of character. Harold Merefield is rarely more than shadowy. At this point in the series, his main function appears to be to try and mislead the reader via his many surmises about the case in question - and like many Watsons, he is occasionally unforgiveably thick. Nor is Dr Priestley himself more than vaguely drawn, being conveyed to the reader chiefly through Rhode harping on the word "testy".

The novel is on firmer ground with Priestley's idiosyncratic approach to crime investigation, and his relentless determination to separate facts from theories, inferences, conclusions and guesses. Particularly interesting is the mathematician's scepticism about the value of eyewitness testimony and the way it can be influenced, as illustrated by the variance in testimony given by a railway ticket-collector before and after he knows that a murder has been committed. In the wake of the second murder, the suspicions of both Dr Priestley and the police - in the form of Inspector Hanslet, who, we gather, gained a reluctant respect for the abilities of the part-time amateur detective during The Paddington Mystery - become focused upon Mrs Milton, Gerald's housekeeper, and his solicitor Mr Withers, both beneficiaries under Gerald's will and, it appears, rather more than "just friends". But while Hanslet pursues his human suspects, Dr Priestley's attention turns to Horn's Lane, where Austin Heatherdale's body was found, and to the features of the surrounding Essex countryside.

As his investigation proceeds, Priestley becomes convinced that the world is looking at the murders of the Heatherdale brothers through a smokescreen, and that a great deal of sleight-of-hand has been perpetrated by the murderer, or murderers, to make the motive and circumstances of their deaths seem other than they really are. While the feints and diversionary tactics succeed in sidetracking the police, Dr Priestley continues with his dogged sifting of the scanty evidence, and finally discards almost everything that is "known" about the death of Austin Heatherdale, from the time of his death, to where it happened, to his last movements during the days leading up to the murder. But in spite of Priestley's own convictions about the case, the facts he seeks remain elusive until a disaster aboard the cargo-ship and a near-escape from tragedy for Captain Murchison supply him with the final pieces of the puzzle...