Grimesby Roylott (The doctor of Stoke Moran): The stepfather who did the math before he let the snake loose

In “The Adventure of the Speckled Band” (Arthur Conan Doyle, 1892), one morning in April 1883, a huge man bursts into the sitting room at Baker Street. He wears a black top hat, a frock coat and high gaiters, and swings a hunting crop; his face is burned yellow by the sun, and Watson thinks he looks like a fierce old bird of prey. He is Dr. Grimesby Roylott, of Stoke Moran, stepfather of Helen Stoner, the young woman who has just left after telling Holmes she is afraid. He demands to know what his stepdaughter has said. Holmes talks about the cold weather and the crocuses. Roylott calls him a meddler, seizes the poker from the fireplace, bends it with his hands and warns him to keep out of his grip. Once he has gone, Holmes straightens the poker and walks to Doctors’ Commons to read the girls’ mother’s will. He comes back with a sheet of blue paper covered in figures. That is the motive.

// The theoryA murder that fits in a ledger

Roylott is the villain of one of the most famous Sherlock Holmes stories: a doctor from a ruined family who lives on his late wife’s income and who, as Holmes discovers, has already killed one of his stepdaughters and is preparing to kill the other. This case file reveals the ending. To read him, a theory that looks for neither trauma nor pathology is useful. In 1968, the economist Gary Becker published “Crime and Punishment: An Economic Approach,” in which he proposed treating crime as a decision: someone commits it if the utility they expect from it exceeds the utility they could get by using their time and resources in other ways. The expected cost is not the punishment, but the punishment multiplied by the probability of suffering it. Isaac Ehrlich extended the model and tested it against data in 1973.

// The subjectThe man who bends pokers

The story presents Roylott in three moments. The first is his past, as Helen tells it: the last of an old Saxon family ruined by four wasteful heirs and a gambler, he studied medicine on a loan, set up a practice in Calcutta and, in a fit of anger over some robberies, beat his butler to death. He narrowly escaped a death sentence and served a long prison term. Back in England, he shuts himself up in the family house, quarrels with the whole village, threw the blacksmith over a parapet into a stream the week before, and lets a cheetah and a baboon roam his grounds. The second is the scene at Baker Street. The third is his bedroom, which Holmes inspects while he is in London: an iron safe with a saucer of milk on top, a chair showing that he has been standing on it, and a dog lash tied into a loop. In the room next door, a bell-rope that does not ring, a ventilator that opens into Roylott’s room and a bed clamped to the floor.

The calendar completes the calculation. Julia, Helen’s twin, died two years earlier, less than two weeks before her wedding to a major of marines, crying out something about a “speckled band.” A month before the visit to Baker Street, Helen became engaged to Percy Armitage. Two days before it, Roylott started repairs on a wall that needed none, and Helen had to move into her sister’s room, to sleep in the very same bed. The night before she came to Baker Street, she heard the whistle Julia had heard. (Spoiler warning.) Holmes and Watson wait in the dark in that room. When a swamp adder comes down the bell-rope, Holmes lashes at it with a cane; the snake goes back through the ventilator and bites its master, who dies within seconds with the serpent coiled round his head like a yellow band with brownish speckles. The official inquiry concludes that the doctor died while carelessly playing with a dangerous pet.

// The crackTwo criminals in one body

Roylott gives Becker an almost laboratory case, and at the same time shows the model’s limits. There are two offenders in him. One is the cold planner of the ventilator, who trains a snake with milk and a whistle and accepts that it may not bite the first night, because sooner or later it will. The other is the man who killed his butler in a fit of rage, who throws blacksmiths into streams and who leaves the marks of four fingers and a thumb on Helen’s wrist. That second Roylott is exactly the kind of violence, impulsive and uncalculated, that the economic model explains worst. And the impulsive man spoils the planner’s arithmetic: by following Helen to London and threatening Holmes, he is the one who sends his own probability of being caught soaring. That is why economists of crime had to speak of bounded rationality: people calculate, but badly, in a hurry and in anger.

Nor does the model say why Roylott settles with a murder what others would settle with a lawsuit, cutting expenses or resignation. Becker leaves it to each person’s preferences, and the story suggests something more concrete: a man who has already killed once, who has been through prison and who lives isolated does not pay the same moral cost as his neighbors. Explaining Roylott is not excusing him. The calculation explains why his stepdaughters’ deaths suited him; it takes nothing away from what he is: a murderer who chose two young women who depended on him.