The boys confronted an arch in the rock, an opening that seemed to lead into a tunnel. They approached it cautiously, and Frank often turned the light on the floor to make sure that no pitfalls lay before them.
Frank went into the tunnel first. In single file, the others followed.
It was about fifteen feet in length and about six feet high. As the floor was of solid rock, they were unable to find any foot-prints that would serve to prove that the intruder had passed that way.
The tunnel led to another cave.
"Why, there's a regular chain of caves in here!" exclaimed Joe, as the boys stepped out into a massive underground chamber.
"Our cave was only the beginning," said Chet.
In the glow of their flashlights they saw that the cave in which they now stood had a number of dark openings in the walls. These were, presumably, tunnels leading into further caves beyond.
"There are a dozen different passages out of here. Our friend might have taken any of them," said Frank.
"We'll tackle the biggest," suggested Biff.
"Good idea. If we don't get anywhere, we'll try the others."