Father Knox was an influential theologian, classical scholar and critic. He is well-known in the mystery field as one of the founders of of Holmesian scholarship as well as the author of the celebrated "ten commandments" for writing detective fiction. These commandments are as follows:
1. The criminal must be mentioned in the early part of the story, but must not be anyone whose thoughts the reader has been allowed to know.
2. All supernatural or preternatural agencies are ruled out as a matter of course.
3. Not more than one secret room or passage is allowed.
4. No hitherto undiscovered poisons may be used, nor any appliance which will need a long scientific explanation at the end.
5. No Chinaman may figure in the story.
6. No accident may help the detective, nor must he have any unaccountable intuition which proves to be right.
7. The detective himself must not commit the crime.
8. The detective is bound to declare any clues which he may discover.
9. The stupid friend of the detective, the Watson, must not conceal from the reader any thoughts which pass through his mind: his intelligence must be slightly, but very slightly below that of the average reader.
10. Twin brothers, and doubles generally, must not appear unless we have been duly prepared for them.
And most writers of the Golden Age followed these rules scrupulously. The Footsteps at the Lock shows Father Knox to be not only a scholar and critic of the genre but one who could practice what he preached.
The story starts out innocently enough. Two cousins, Derek and Nigel Burtell, set out on a canoeing trip up the Thames. The goal is to give Derek a voyage in the great outdoors to restore his failing health. It also happens that Derek is shortly, upon his 25th birthday, to inherit 50,000 pounds from his grandfather. Insurance is also involved because, in view of Derek's frail condition, his life has been insured by the Indescribable Insurance Company in the event that he does not reach the celebrated day.
While the journey upstream is uneventful, the return trip does not go as planned. Nigel must leave the canoe at Shipcote Lock in order to take an exam at Oxford. While he is away, the canoe is found adrift below the lock, Derek has disappeared, and there is a jagged gash in the bottom of the canoe. The Indescribable Insurance Company immediately suspects foul play and sends Miles Bredon, a prime investigator, to investigate the circumstances. Is there a murderer along the banks of the Thames or has Derek met with an unfortunate accident? Most importantly, will the company have to acknowledge the claim? Further muddying the waters, Derek's cousin has disappeared as well.
This is a very literate and witty mystery. And very tongue-in-cheek. There are plenty of clues from a set of strange photographs to a baffling cipher to the trail of footprints near the lock and there is also plenty of opportunity to match wits with Bredon. The challenging mystery and nefarious deeds are countered with the beautiful descriptions of the river and the surrounding countryside.
It has been a while since I read this one, but I do remember enjoying the interactions between Mike Bredon and his wife, Angela. They set out by canoe to retrace the cousins' trip and to investigate the area around the lock. Angela is a good partner for Mike and there is a fair amount of witty conversation.