We got into two of the waiting motorcars⁠—all but Sir Walter, who went off to Scotland Yard⁠—to “mobilize MacGillivray,” so he said. We marched through empty corridors and big bare chambers where the charwomen were busy, till we reached a little room lined with books and maps. A resident clerk was unearthed, who presently fetched from the library the Admiralty Tide Tables. I sat at the desk and the others stood round, for somehow or other I had got charge of this expedition.

It was no good. There were hundreds of entries, and so far as I could see 10:17 might cover fifty places. We had to find some way of narrowing the possibilities.

I took my head in my hands and thought. There must be some way of reading this riddle. What did Scudder mean by steps? I thought of dock steps, but if he had meant that I didn’t think he would have mentioned the number. It must be some place where there were several staircases, and one marked out from the others by having thirty-nine steps.