“Don’t trouble it,” said Frank. ‪“It may let us down into another underground lake.”

‪“Do you believe it?”

‪“I should fear it.”

But Tony could not resist the temptation to insert his fingers in the ring and give the stone a lift. It was a reckless thing to do.

The result was startling.

The stone yielded, and the next moment Buckden lifted it from its bed, disclosing a cavity beneath some four feet long by two wide.

Stone steps were revealed leading downward. For a moment the two explorers looked at each other.

‪“What will we do?” asked Buckden.

‪“Investigate,” said Frank, tersely.

‪“But it is dark down there.”