We entered the cave, and he flung his pack into a corner. “Last time I was here,” he said, “I covered the floor with heather. We must get some more if we would sleep soft.” In the twilight he was a dim figure, but he seemed a new man from the one I had last seen in the Moot Hall at Biggleswick. There was a wiry vigour in his body and a purpose in his face. What a fool I had been to set him down as no more than a conceited flâneur!

He went out to the shelf again and sniffed the fresh evening. There was a wonderful red sky in the west, but in the crevice the shades had fallen, and only the bright patches at either end told of the sunset.

“Wake,” I said, “you and I have to understand each other. I’m a friend of Ivery and I know the meaning of this place. I discovered it by accident, but I want you to know that I’m heart and soul with you. You may trust me in tonight’s job as if I were Ivery himself.”

He swung round and looked at me sharply. His eyes were hot again, as I remembered them at our first meeting.

“What do you mean? How much do you know?”

The hammer was going hard in my forehead, and I had to pull myself together to answer.

“I know that at the end of this crack a message was left last night, and that someone came out of the sea and picked it up. That someone is coming again when darkness falls, and there will be another message.”

He had turned his head away. “You are talking nonsense. No submarine could land on this coast.”

I could see that he was trying me.

“This morning,” I said, “I swam in the deep-water inlet below us. It is the most perfect submarine shelter in Britain.”