Tad Butler, however, knew that imagination had played no part in this voice. He had heard the voice before. He informed his companions of this fact.

"Heard it before? Where?" exclaimed Ned.

"On top of the Ruby Mountain yesterday," answered the boy.

CHAPTER XXIII

IN THE RUBY MOUNTAIN

Tom Phipps nodded. He recalled his conversation with Tad upon the other's upon his return from his visit to the Ruby Mountain, and the lad's description of the mysterious voice he had heard there. Mr.

Phipps did not give very serious consideration to that part of the boy's story at the time. Now, however, he was startled beyond words.

All of them were startled. To hear a strange voice many feet down under the ground, when all supposed they were far beyond the reach of a human voice, was enough to give almost anyone a start.

Yet Tad was not as much surprised as were his companions, for it will be remembered he already had been through the experience that was so new to the others.

"Who are you?" demanded Mr. Phipps almost sternly.

There was no reply to his question.

"Tad, are you sure that is the same voice?"

"Positive. There can be no doubt. And, besides, she has used the same words."

"But it's impossible," insisted the young engineer. "No one, let alone a woman, could get near enough to this chamber to be heard as distinctly as that."

"I--I think it must be somebody who can go right through a rock,"

stammered Ned.

"Ghosts," nodded Walter.

"That's what I thought at first. But I knew it couldn't be after I had time to think twice. And I--"

"He-l-l-l-o-o-o!"

"There it goes again," fairly shouted Tom Phipps. "I'm going to find out what this means before I'm another minute older."

Hastily lighting a match he made a tour of the chamber, every corner of which he examined carefully, ending by a long, critical survey of the hole in the roof.

"It is just as impossible for anyone to be up there as it is to expect to see some one walk through the solid rocks here beside us," he decided, throwing the spent match on the floor where it glowed briefly and went out, leaving the darkness more dense than before.

Tad struck a fresh match.

"h.e.l.lo, what's this?" he cried, reaching for a small package that lay wrapped in a piece of newspaper on the floor near him. "I didn't see that before."

"Doughnuts!" shouted Ned, who had been peering curiously over Tad's shoulder as the latter opened the package.

"Yes, and they are real," exulted Tad. Already one of them was in his mouth, and the others of the party quickly helped themselves. There was just enough to go around.

"I don't care who you are, but we're much obliged just the same,"

called Ned in a m.u.f.fled voice.

"Yes, there's nothing ghostly about this 'bear sign,'" added Tad.

As for their companion, Tom Phipps, words failed him.

"I'm sure I'm going crazy now," he said. "If you are real, for goodness' sake tell us who you are and where you are?" he pleaded.

A merry, chuckling laugh answered him.

"She's up there!" said Tad Butler sharply. He had been listening with every sense on the alert, determined to locate the owner of the voice when next she spoke. Now he was sure that he had succeeded. "I know where you are but I don't know how you ever got there."

"Do you know a way out of this?" interjected Walter.

"Of course," answered the girl.

Tad nodded to his companions. They were burning up their matches very fast now in an effort to catch sight of the owner of the voice.

"How did you suppose I got there if I didn't know the way?"

"No ghost about that, I guess," said the boy.

"Will you help us to get out of here?" asked Tom.

"Can't."

"Why not?" demanded Ned.

"Can you climb up here?"

"No, certainly not."

"Well, that's the answer."

They laughed in spite of themselves.

"Will you tell us how you got where you are?" asked Mr. Phipps.

"That's a secret," replied the girl.

"And I presume your name is a secret too?"

"Yes."

"We'll find out who you are when we get out of here. I promise you that," threatened the a.s.sistant superintendent.