"No!" screamed Cora.

"In there with you or I'll--"

He looked so terrible, and made such a threatening gesture, and the half-witted youth seemed so ready to do his master's bidding that the girls shrank back from the claw-like hands of the old man, and fairly ran into the secret room opened by the helper. Once inside they heard the door close after them.

"Oh!" gasped Belle. "This is terrible, Cora! What shall we do?"

"Keep quiet a minute. Let me think. Oh, oh!"

Hazel flashed on her light.

"Thank heaven for that!" moaned Belle. "We can at least see."

The girls looked quickly about them. The light showed them that they were in some sort of office. There were desks and chairs in it, and on the desk were a number of papers, while innumerable tickets were scattered about. The girls attached no significance to them at first.

There was an incandescent lamp swinging above the desk, and Cora turned the black key. At once there was light, showing that the gasoline engine, the rumble of which could still be heard, operated a small dynamo.

"Oh, what shall we do?" gasped Bess.

"Listen!" whispered Cora.

From the cave outside came the murmur of excited and angry voices. There followed sounds of great activity, as if boxes and barrels were being moved about. Once or twice came a snarl from the idiot, and the commanding voice of the old man. The other voices the girls could not recognize.

"I'm going to call for help," said Cora. "That may be the boys come to rescue us. Come on, girls! We'll all shriek!"

This they did, uniting their shrill voices in an appeal for help. Cora caught up a paper-weight from the desk and hammered on the door of their prison. But neither their calls nor the pounding brought an answer. The noise in the outer cave continued. The men seemed to be quarreling among themselves now.

Then came silence. The girls called again but with no result. They listened. Not a sound came from beyond the door.

"What has happened?" asked Bess.

"I can't even guess," Cora said. "But don't worry. We'll get out of here some time. Meanwhile, let's see if we can by any means open the door."

Events were now happening in several different places-events connected with the boys and the counterfeiters.

Jack was waiting in his hiding place, wondering what would next take place, and he was getting rather tired of his cramped position, when he heard footsteps coming back.

"Here's where I do a sleuthing act and follow them," he decided. But he was hardly prepared for what followed. The footsteps broke into a run, and there were excited voices calling one to another. There was the crash of falling boxes, and above everything came a strange unearthly yell, like that of some animal in pain.

"What in the world--" began Jack.

There was a rush of several bodies past his hiding place. Jack looked up over the head of the barrel in time to see four men, one carrying a lantern, dash along the cave, and behind them came another with abnormally long arms.

Pausing a moment to allow the fleeing ones to get a little ahead, Jack followed. His brain was excitedly thinking.

"There'll be a grand ruction in a minute," Jack chuckled to himself.

"Things will happen with a vengeance."

He heard cries of rage from the shack at the mouth of the cave.

Advancing into it, but keeping himself concealed, Jack peered out. He noted that the automobile was gone, and from the absence of Paul and Walter he argued that they had driven away in it.

The talk of the men confirmed this.

"They've dished us!" exclaimed one, angrily.

"The car's gone!" faltered another. "We were too slow!"

"What are we going to do?" asked a third.

"Cut and run for it!" some one answered. "The game is up. Scatter, and we'll meet again, later. Lively's the word!"

Jack looked out to see the two men he and his chums had observed before, with a third one, start for the wooded slope of the mountain. Then he saw the old man and the half-witted helper.

"Wait-wait for me!" pleaded the aged one. "I can't run fast, I'm all crippled with rheumatism! Wait!"

"We can't wait. Look out for yourself," one man flung back unfeelingly over his shoulder. "It's every one for himself."

"Ah! desert me, would you!" cried the old man, shaking his fist at the fleeing ones. "But I'll get even with you. Old Jason will get even! I'll let the girls out of the cave, and tell them the whole story! I'll let the girls out of the secret room in the cave!"

Jack had been in two minds whether to advance and speak to the old man, or follow the fleeing ones, but as he heard these words he knew something else now called for his attention.

"The girls in the cave!" he murmured. "It must be Cora and the others he means. They must have gone into the cave while we were in town. I've got to rescue them. Let the men go! I must help the girls."

Catching up his lantern, Jack dashed back into the dark cavern.

"I'm coming, girls! I'm coming!" he cried. "To the rescue!"

CHAPTER x.x.x-ALL'S WELL

Walter and Paul, hurrying to aid Jack, whom they had left in the cave, came in sight of the shack just as the old man and his helper were turning back into it. The two boys did not glimpse the three fleeing men who had by this time disappeared among the trees.

"Look-look at that!" gasped Paul, rubbing his eyes. "Am I dreaming, Wally, or is that an ape or a human being?"

"It's real enough-some sort of a crazy chap, I should say. But what's he doing?"

"Calling down the vengeance of heaven, I guess," observed Paul, for they saw the old man shaking his fist in the air.

"Hurry up and we'll speak to him," urged Walter. "Somehow I think he's part of the mystery."

They reached the old man just as he was turning back into the shack. He did not seem greatly surprised to see them.

"Will that-er-fellow hurt us?" asked Walter.

"Not unless I tell him to. Are you the police?"