covered the big plain. They found a few ruins of the ancient city of Poltec.
"Well, what about it?" asked Ned one night as they sat in the balloon, talking it over. "What next, Tom?"
"We've got to keep at it, that's all. I think we'll go up in the balloon, circle around over the plain at just a little elevation, and maybe we can spot it that way."
"All right, I'm with you."
But they did not try that plan. For in the middle of the night Ned suddenly awakened. Something had come to him in his sleep.
"Tom! Tom!" he cried. "I have it! What chumps we were!"
"What's the matter, old man?" asked Tom anxiously. "Are you sick—talking in your sleep?"
"Sleep nothing! I've just thought of it. That tunnel entrance is inside the temple. That's the most natural place in the world for it. I'll bet it's right in the middle of the big inner chamber, where the priests could control it. Why didn't we look there before?"
"That's right; why didn't we?" agreed Tom. "I believe you're right, Ned! We'll look the first thing in the morning."
They did not wait for breakfast before trying
