“Do not delay, Barin, I beg — you have far to go before the dawn. Look, your comrade is already waiting.” Rex was half-buried in the tunnel.

De Richleau took Yakovkin’s horny hand. “I shall not forget,” he said.

The kazak withdrew his hand quickly and kissed the Duke in the old fashion on the left shoulder. “The heart of Russia is ever the heart of Russia,” he murmured, cryptically, and De Richleau followed Rex feet foremost into the hole.

The tunnel was no more than six feet deep, and as it ended Rex dropped with a thud from the ceiling to the floor of the cave.

“Look out,” he called, and was just in time to save the Duke from an eight foot fall.

De Richleau had the torch and Rex the ball of twine.

“Where’ll we make this fast?” the latter asked.

“You have the marlinspike,” said the Duke, “dig it firmly into the earth and tie the end to that.”

“No, that’ll be handy for a weapon,” Rex objected. “Here, this’ll serve — show us a light.” An ancient stone coffin lid lay at their feet. Rex prised it up, got the twine underneath, and tied it firmly. “O.K.,” he announced.

The shaft of light from the Duke’s torch pierced the thick, heavy darkness. The cave had the hot, dry atmosphere of an airless room when the central heating has been left on. They proceeded slowly along the passage, shining the torch to either side, fearful that they might miss the turning in the thick, hot gloom.