“Any of them. None.” His spectacles caught the light as he shook his head. “He would never talk about it.”

It was by now late, and I could see little sense in playing Twenty Questions with a man who could describe the object only by its outline. Holmes clearly felt the same, for he reached out to knock his pipe decisively into an ash-tray.

“Mr Long—” he began to say.

“There is one other thing,” Long interrupted, and Holmes obediently settled back. “Again I do not know what it means, but your father came to see mine in the middle of September 1914. Two weeks before he died. They talked for a long time, and when he left, my father was quiet, but somehow as if a burden had been lifted from him. And when they shook hands, they seemed friends again, as they had not for some time.”

“But you don't know what they talked about.”

“They walked across to the park and sat on a bench, going silent whenever another person came near.”

“Well, thank you, Mr Long,” I said, wishing I did not feel so dissatisfied.

“If we think of any questions, Mr Long,” Holmes said, “may we call on you in your shop?”

“Either I will be there, or my assistant will know where I have gone.”

“Let me go downstairs with you and arrange a motor to take you back. It is late, and your arm clearly troubles you.”

Long protested that it was but a short walk, but Holmes would not be swayed. He retrieved our guest's hat, standing at the ready should the man have any difficulty rising from his chair. He did not, although as Holmes had said, the wounded arm gave all indications of paining him. By way of support, Long gingerly worked his hand into the pocket of his jacket, but when he had done so, he paused, and drew the hand laboriously out again. In his fingers was a paper-wrapped object the shape of a very short cigar, secured in neatly tied twine, which he held out to me.

“In the turmoil of the past few hours, I forgot to give this to you. My father said that it was an object precious to your mother, and removed it for safe-keeping, lest vandals take it.”

I turned the object over in my hands and saw, in a precise, spidery hand:

Inside the paper lay the front door's mezuzah.

Whatever Long saw in my face caused him to take a half-step forward as if to grasp my arm, but he wavered, and instead merely asked, “I hope my father's actions did not create problems for you. He seemed to think it was a kind of household god, perhaps not literally but—”

“No,” I said, my hand closing tightly around the cool metal. “It's fine. I'm very glad to find it safe. Thank you.”