The Puzzle Lock

I do not remember what was the occasion of my dining with Thorndyke at Giamborini's on the particular evening that is now in my mind. Doubtless, some piece of work completed had seemed to justify the modest festival. At any rate, there we were, seated at a somewhat retired table, selected by Thorndyke, with our backs to the large window through which the late June sunlight streamed. We had made our preliminary arrangements, including a bottle of Barsac, and were inspecting dubiously a collection of semi-edible hors d'oeuvres, when a man entered and took possession of a table just in front of ours, which had apparently been reserved for him, since he walked directly to it and drew away the single chair that had been set aslant against it.