"Wonder if any of our fellows will be over to-night," remarked the airman. "We don't give Fritz much rest."
"It's been quieter to-day than ever since I've been here," said Alec. "You were the last fellow to come over."
"And stay here," added the other grimly. "Hope Fritz doesn't think that one man being brought down will put the others off. If so, he's vastly mistaken."
"I wish there would be a big raid or bombardment," declared the Sub. "We'd have to run the risk of being strafed; but, on the other hand, Fritz would be much too busy to worry about us. What's the weight of this stone: three-quarters of a hundredweight?"
"Quite," replied Smith promptly. He had been mentally calculating the cubic capacity and weight of that wedge-shaped piece of stone for hours past. "It's not the weight that matters so much. It's the awkward shape of the brute."
For the next ten minutes the two toilers were silent. Every jab with the now-blunted marline-spike was telling. The stone was almost ready for removal.
"Hist!" whispered Seton, holding up a warning hand. Although it was night, the stars enabled the men, accustomed to the sombre conditions, to see with comparative ease.
"What is it?" whispered Smith.
In reply Seton inserted the point of the spike into a crevice and pressed his ear lightly against the blunt end. His suspicions were not ill-founded. The metal, acting as a transmitter of sound, enabled him to detect footsteps in the corridor beneath.
"Rough luck," remarked the pilot in a low tone.