“Well, gentlemen, I can’t think of anywhere else. Of course, there’s the Ruff⁠—”

“What’s that?” I asked.

“The big chalk headland in Kent, close to Bradgate. It’s got a lot of villas on the top, and some of the houses have staircases down to a private beach. It’s a very high-toned sort of place, and the residents there like to keep by themselves.”

I tore open the Tide Tables and found Bradgate. High tide there was at 10:27 p.m. on the 15th of June .

“We’re on the scent at last,” I cried excitedly. “How can I find out what is the tide at the Ruff?”

“I can tell you that, sir,” said the coastguard man. “I once was lent a house there in this very month, and I used to go out at night to the deep-sea fishing. The tide’s ten minutes before Bradgate.”

I closed the book and looked round at the company.

“If one of those staircases has thirty-nine steps we have solved the mystery, gentlemen,” I said. “I want the loan of your car, Sir Walter, and a map of the roads. If Mr. MacGillivray will spare me ten minutes, I think we can prepare something for tomorrow.”

It was ridiculous in me to take charge of the business like this, but they didn’t seem to mind, and after all I had been in the show from the start. Besides, I was used to rough jobs, and these eminent gentlemen were too clever not to see it. It was General Royer who gave me my commission. “I for one,” he said, “am content to leave the matter in Mr. Hannay’s hands.”