Then I had a sudden thought, and hunted up all the steamer sailings. There was no boat which left for the Continent at 10:17 p.m.

Why was high tide so important? If it was a harbour it must be some little place where the tide mattered, or else it was a heavy-draught boat. But there was no regular steamer sailing at that hour, and somehow I didn’t think they would travel by a big boat from a regular harbour. So it must be some little harbour where the tide was important, or perhaps no harbour at all.

But if it was a little port I couldn’t see what the steps signified. There were no sets of staircases on any harbour that I had ever seen. It must be some place which a particular staircase identified, and where the tide was full at 10:17. On the whole it seemed to me that the place must be a bit of open coast. But the staircases kept puzzling me.