"There is also, I fancy, in the neighbourhood, a spur of rock running out into the sea, quite possibly with a handy diving-pool. It must run out pretty far; at any rate, one can bathe there before it is high water on the beach."
"I don't know how you know that, sir, but it's a fact. There's rocks and a bathing-pool, exactly as you describe, about a hundred yards farther along. Many's the time I've had a dip off the end of them."
"And the rocks run right back inland, where they are covered with short grass."
"That's right."
"The murder took place shortly before high tide, I fancy, and the body lay just about at high-tide mark."
"Why so?"
"Well, you say there were footsteps leading right up to the body. That means that the water hadn't been up beyond the body. But there were no other marks. Therefore the murderer's footprints must have been washed away by the tide. The only explanation is that the two men were standing together just below the tide-mark. The murderer came up out of the sea. He attacked the other man—maybe he forced him back a little on his own tracks—and there he killed him. Then the water came up and washed out any marks the murderer may have left. One can imagine him squatting there, wondering if the sea was going to come up high enough."
"Ow!" said Kitty, "you make me creep all over."
"Now, as to these marks on the face," pursued the first-class passenger. "The murderer, according to the idea I get of the thing, was already in the sea when the victim came along. You see the idea?"
"I get you," said the stout man. "You think as he went in off them rocks what we was speaking of, and came up through the water, and that's why there weren't no footprints."