“Breakfust!  Breakfust!” called Eradicate, when Tom was about to start on a second round.

“Let’s eat,” suggested Ned, “and then we four can circle around together.”  Tom agreed that this would be a good plan.  A little later then, with Tom nearest the temple walls, the four began their march around them.

Four times that morning they made the circuit, and the same number in the afternoon, until they were nearly half a mile away from the ruin, but no tunnel showed.

“Well, we’ll have to keep at it to-morrow,” suggested Tom.  “It’s too soon to give up.”

But the morrow brought no better success, nor did the following two days.  In fact for a week they kept up the search for the tunnel, but did not come upon it, and they had now pretty well 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 the experiment, and Mr. Damon and Eradicate went with Tom and Ned.  It was no easy work to make their way over the ruins to the inner auditorium.  Wreckage and ruin was all around, and they had to avoid the yawning holes on every side.  But when they got to the main, or sacrificial chamber, as Ned insisted on calling it, they found the floor there solid.  In the centre was a great altar, but to their chagrin there was not a sign of a tunnel opening.

“Fooled again!” said Tom bitterly.

“Maybe some of those holes outside is the entrance,” suggested Mr. Damon.

“I don’t believe so,” objected Tom.  “They seemed to go only to the cellar, if a temple has such a thing.”

Bitterly disappointed, Tom strolled over and stood in front of the big stone altar.  It seemed that he must give up the search.  Idly he looked at the sacrificial stone.  Projecting from it was a sort of a bundle.

Tom took hold of it, and to his surprise he found that it could be moved.  Hardly knowing what he was doing, he pulled it toward him.