“Go carefully,” cautioned Mr. Henderson, “Watch on all sides and up above.  Better let Andy and me go ahead.”

The scientist and the old hunter led the way.  Through the arch they went, and emerged into what must at one time have been a magnificent courtyard.  Before them was the temple proper, a vast structure, with an opening through which fifty men might have marched abreast.  But the doors were gone, and the portal was but a black hole.

“I hope there ain’t any ghosts in there,” said Washington, with a shiver.

“Nonsense!” exclaimed the professor.  “There may be things as bad, but there are no such things as ghosts.  Have your gun ready, Andy.”

With every sense on the alert, the old hunter advanced.  Every one was a bit nervous, and, as Mark and Jack afterward admitted, they half expected some terrible beast to rush out at them.  But nothing of the kind happened, and they went into the interior of the temple.

At first it was so dark they could see nothing.  There were vast dim shapes on every side, and from the hollow echo of their footsteps they judged the roof must be very high and the structure big in every way.

Then, as their eyes became used to the darkness, they could make out, up front, something like an altar or pulpit.

“Perhaps that’s where they offered up the gold and diamonds as a sacrifice to their gods,” spoke Mark in a whisper.

“Sacrifice to their gods!” came back a hundred echoes and the sound made every one shudder.

“Oh!” said Washington, in a low voice.

“Oh!  Oh!  Oh!” repeated the echoes in voices of thunder.

“Well, this is pleasant,” spoke Andy, in his natural tones, and, to the surprise of all there was no echo.  It was only when a person whispered or spoke low that the sound was heard.  After that they talked naturally.

“You stay here, and Andy and I will go up front and see what there is,” said Mr. Henderson.  “Be on your guard, and if you hear us coming back in a hurry, run!”

It was with no little feeling of nervousness that the boys, Bill, Tom and Washington watched the two men move off in the darkness.  They could hear their footsteps on the stone flags and could dimly see them.

“They must be almost to the altar by this time,” said Mark, after a long pause.

Hardly had he spoken than there came a loud, sound from where Mr. Henderson and Andy had gone.  It was as if some giant wings were beating the air.  Then came shrill cries and the voice of the old hunter could be heard calling: 

“Kneel down, Professor!  Let me get a shot at the brute!”

Those waiting in the rear of the temple huddled closer together.  What terrible beast could have been aroused?

The next instant the place seemed illuminated as if by a lightning flash, and a sound as of a thousand thunder claps resounded.

“I think I winged him!” cried Andy’s voice, and the boys knew he had fired at something.