They had all heard something different, it developed. At least, they all had a different impression of the noise.

Cora described it as a "trembling roar."

Bess said it was a rumble, as though a heavy wagon had pa.s.sed in front of the bungalow.

Belle said it reminded her of a deep, heavy sound, such as she had once heard in a blast furnace.

It was reserved for Hazel to describe accurately the noise, though none of them knew her description was correct until afterward.

"It was like a factory or machine shop next door," said Paul's sister.

"It seemed to shake the bungalow as though heavy machinery were working."

"It must be the waterfall," decided Jack. "Only a large body of water, tumbling down into some chasm, could make a noise like that. There's no machinery around here. Besides, the waterfall is bigger than ever now, on account of the rain. It must be that."

"It wasn't!" declared Cora, though when pressed for reasons to bolster up her denial she could give none. "It wasn't that sort of noise at all," she affirmed. "It was more like--"

"What's that?" asked Belle so suddenly that the other girls jumped nervously.

It was the sound of a footstep on the porch, a firm, unhesitating footstep.

"I expect that's my husband," said Mrs. Floyd.

It was Mr. Floyd, and he was, greatly surprised to see the "whole family up," as he expressed it.

"What's the matter?" he asked, looking around on the circle of rather startled faces, ending with his wife's. "Did you sit up to see how late I got in? Strictly business, young ladies and gentlemen," he went on, smiling at them. "The committee had considerable to transact, and I had to stay."

"This is a sort of surprise party," Cora told him. "Camp Surprise is living up to its name," and she went on to tell about the noise, the others adding bits here and there.

"Pshaw now! That's queer!" commented Mr. Floyd. "I have heard them rumblings myself, but I laid 'em to the waterfall. It's a curious cataract at times."

"This noise," began Cora, "isn't like anything I ever--"

She paused midway in the sentence, and a strange look grew and spread over her face, as it did over the faces of the others.

"There it is now," whispered Bess. "That-that noise!"

They all heard it, a dull, rumbling roar that made the bungalow tremble as when a heavy wind blows and vibrates the timbers of a house.

"So that's what it is!" exclaimed Jack. "This is my first experience."

"I heard it once, though distantly," said Walter.

"Listen!" cautioned Cora.

The noise seemed to increase.

"Say, that is curious!" commented Mr. Floyd. "I never noticed that before. Where does it come from?"

Hardly had he spoken than the rumbling ceased, and there came a sharp crash, as though wood had broken somewhere.

"The chimney's fallen!" cried Mrs. Floyd.

"Nonsense, Eliza," said her husband. "The crash would be up on the roof if the chimney toppled over. Besides, there's no wind, and the noise didn't come from above, it came from-down there!"

He pointed to the floor of the living room, which was of bare boards, with rugs here and there.

"That's right!" cried Jack. "The crash was below us. It's under this bungalow somewhere. Up with the floor boards! We'll get at the bottom of this!"

There was no doubt on that score. Every one in the room was sure the noise had come from under the floor.

"But how could it?" asked Walter. "There's no cellar to the bungalow; is there?"

"None that I ever heard of," said Mr. Floyd. "I didn't live here when the bungalow was built, but I've always understood it had no cellar."

"It hasn't," Cora affirmed. "At least none that you can find. There are no cellar stairs and the place seems to rest on piles."

"But the noise came from down there," and Jack pointed to the floor.

"The only way to find out is to take up the boards. May we, Mr. Floyd?"

"Why, yes, I reckon so. We've got to get at the bottom of this. It's better to spoil the floor than to lose the renting of the bungalow by ghosts scaring tenants away. Take up the boards. I'll get an axe and a crowbar."

And so, in the middle of the night, for it was close to twelve o'clock, the strange work of looking under the floor of the bungalow for the source of the queer noise was begun.

"Where shall we start?" asked Jack, when Mr. Floyd had brought the implements.

The caretaker considered a moment.

"If there is some sort of cellar, or s.p.a.ce under this bungalow, it must be near the center of the floor, I'm thinking. We'll begin there. Don't be afraid of spoiling the floor. I'll take the responsibility."

Jack swung the axe vigorously, and, being aided by Walter, soon had removed two or three of the narrow boards. As they were prying on another, a queer thing happened.

A solid section of the floor from the middle of the room suddenly sank down, and then rolled back, exactly as a sliding door rolls, only this door was horizontal instead of vertical. Back it rolled, leaving what was practically a trap in the floor, and as the light shone down this a flight of steps was revealed leading into darkness.

"Great b.u.mblebees!" gasped Jack. "See what we've done! Uncovered a secret pa.s.sage! Now for the solution of the mystery!"

CHAPTER XXV-THE PATCHED TIRE

Crowding around Jack they all gazed down into the opening. For a moment no one spoke. Then Cora softly murmured:

"A secret pa.s.sage."

"What else is it?" demanded her brother. "No one knew it was here. You didn't; did you?" he asked Mr. Floyd.

"Never had the least notion of it. How it got here is a mystery to me."