“Yes, I see.” Rutledge gingerly tested an edge, and could see that it was quite remarkably sharp still. “Where did you say it was found?”

“I didn’t. But from what I was told, the old grandfather lived in East Anglia. There’s flint there, along the north coast.” He reached into the case again and drew out two or three unprepossessing round gray stones, and with them half of a stone, showing the shiny black surface of the flint inside. Rutledge was well aware of what flint looked like. But he let the proprietor continue his explanation of how flint tools could be made. “Stone Age or not, but whoever discovered how to do this sort of work must have had a monopoly in his day. Everyone came to him for their blades. Until someone else learned how to do it a little better or a little faster. Striking the blow in the right place to make a sharp edge rather than break the edge off—that’s the skill right there.”

Rutledge said after a moment, “A long way to come, to sell you this find.”

“I was of the same opinion.” The man shrugged. “But it’s a fine piece of its kind. Only it never sold. There’s not much call for something this old. I’ve kept it more as a curiosity than anything else. What’s a military shop without what must have been one of the first tools of war?”

“How do you remember who brought you each item?” Rutledge asked.

“I’ve kept a record over the years. I read it sometimes. There was a gilded sword that had belonged to one of Napoleon’s generals. Inscribed as well. I was reluctant to sell it, but money is money.”

He pulled a dog-eared ledger from beneath his counter and opened it at random. Rutledge could see that he had listed each object he’d bought, the date, and the price paid. He’d also drawn a fine sketch of it as well. “Let’s see.” He thumbed through the pages until he’d found what he wanted. “There it is: 1908. Flint knife blade.” He pointed to the clever sketch, filled in with black ink. “Sold to me for fifteen pounds by a Charles Henry. No provenance that it is as old as it appears to be, but it is a fine example of flint workmanship, and I rather liked it. But it never brought in the profit I had anticipated.” He turned more pages, and then pointed out that he had sold a button hook to a man from Kent on holiday in Hastings. “This is the half of the ledger where I keep my sales listed.”

Rutledge thanked the man and was on the point of leaving when he changed his mind and asked the price of the flint knife.

“Sixteen pounds, I’m afraid. Necessary to turn a profit even after all this time.”

Rutledge bought it, and then asked if it could be wrapped and put into a box for mailing.

Ten minutes later, he walked out of the shop and went to find the post office. There he sent the small parcel to Chief Inspector Cummins.