He sat down at the table and began methodically to rule the pages each into three columns, two quite narrow and one broad. The process occupied some time, during which I sat and watched with impatient curiosity the unhurried, precise movements of Thorndyke’s pencil, all agog to hear the promised explanation. He was just finishing the last page when there came a gentle tap at the door, and Polton entered with a satisfied smile on his dry, shrewd-looking face and a small board in his hand.

“Will this do, sir?” he asked.

As he spoke he handed the little board to Thorndyke, who looked at it and passed it to me.

“The very thing, Polton,” my friend replied. “Where did you find it? It’s of no use for you to pretend that you’ve made it in about two minutes and a half.”

Polton smiled one of his queer crinkly smiles, and remarking that “it didn’t take much making,” departed much gratified by the compliment.