One of the things which I disliked about the second Dr. Thorndyke novel, The Eye of Osiris, is that all of the principal characters were Materialists. (For those not familiar: materialism, in this sense, is the belief that the only thing which exists is matter and its interactions; it denies things like God, the soul, free will, etc.) While the characters were not religious in the first book, it was far more explicit here and the book was, in consequence, less enjoyable.
The main problem with Materialists as detectives is that their position is a false one with regard to the main activities of a detective. A detective detects, yes, but for a purpose. In a mystery, the world has become corrupted through the wrong use of reason, and the detective enters it in order to restore the world to its proper order through the right use of reason. It is true that detective stories sometimes aimed to be pure puzzles, as if they were a long-form version of a logic problem where “The baker is sitting next to the red haired man, and across from Sally”. That is simply false, though. The moment that there are characters who are moving through time, they must have motives; they must have a theory of the world and be acting according to it or against it, and thinking well of themselves or being self-reproachful. In short, once you have characters not not mere chess-pieces, they must be human. They might be failed human beings, as in the classic creature of pure habit who goes to work, comes home, watches TV until it’s bedtime, and repeats the process every day merely because it is his habit, with no more thought than we can perceive a rabbit gives to munching grass. But the very fact of telling us what a man does during the day tells us what he doesn’t do, by exclusion. In short, the pure puzzle does not work.
The Materialist cannot do anything other than a pure puzzle. To the Materialist, a human being is merely a clump of matter that happens to be more interesting than an equally sized clod of dirt for reasons of pure sentimentality. The mystery cannot actually be a problem, to the Materialist, because he has no theory of the world in which one organization of matter is superior to any other. He cannot be restoring the world to its proper order because it has no proper order. The Materialist, in truth, has no reason to do one thing instead of another; all he has are the tendencies he has inherited from men who did have a reason to get out of bed in the morning.
This problem is exacerbated in The Eye of Osiris because the person whom Dr. Thorndyke is helping cannot pay Dr. Thorndyke’s fee. Some reason must be put forth for Dr. Thorndyke helping, and since charity is not a permissible reason, as Materialists may neither give nor receive charity for reasons a little too involved to go into here, Dr. Thorndyke is in the absurd position of insisting that he is not in the least helping the old man intentionally, but purely as a by-product of satisfying his own curiosity in the case. In fact, he goes so far as to reject the old man’s thanks.
This is reasonably true to life; Materialists cannot actually exist in society with other Materialists, because their mutual philosophy leaves no room for human beings. It is not, however, interesting. The wretched state of the Materialist is true, so in that sense the book does embody a truth about real life, but it is an unpleasant truth. Unpleasant truths are not what we look for in mystery novels. We look to mystery novels, not for the temporary truth that the world has fallen, but for the eternal truth that the world has been saved. It’s hard enough to remember in this world of sin and woe; we don’t need our reminders of it to make it harder to remember.