"What?"

"His prison, sah."

"If you don't tell where it is, we shall shoot you, sir!"

As Old King Brady made this threat he pushed his revolver against Nick's forehead, and the c.o.o.n gave a wild yell of terror.

"Fo' hebbin's sake," he groaned, "doan fire!"

"I'll solve the mystery of this swamp, or I'll murder you!" fiercely cried the old detective. "Do you hear me, sir?"

A cold sweat burst out all over the darky.

He gazed around in alarm, and gasped hoa.r.s.ely:

"If I tell, will yo' gib me away?"

"To whom?"

"Ma.s.sa Mason."

"Of course not."

"Den listen. Dar's a tunnel under de flo' ob dat hut."

"Where does it lead to?"

"A big cave under de island in de swamp."

"How do you reach it?"

"Froo a trap-doo' in one corner, covered wid earf."

"And that's where Mason is keeping his prisoner, eh?"

"Ya.s.sah. We free lib dar."

"Is that where you carried Dalton on the night you took him from the cars?" demanded Old King Brady.

"Ob co'se," replied the c.o.o.n. "An' if Mason find out dat I done tell yo' about it, 'spect he'd kill me like a dog."

"No doubt he would," said the old detective. "He is capable of doing almost any kind of villainy. Where were you to-night?"

"Bringin' food fo' de cave, as our supply ran out."

"I thought as much."

Just then Harry muttered:

"Well, the great swamp mystery turns out to be a very simple matter, now that we fully understand it, Old King Brady."

"This man may be lying, Harry."

"We can easily prove what he has told us."

"Yes, indeed. And if we find Mr. Dalton kept a prisoner it will go mighty hard with Mason when we capture him. I'm glad to hear that the old broker had the nerve to resist his demands, for it looks to me as if his nephew were trying to ama.s.s all the money he can get his hands on in order to escape from here as soon as possible."

They questioned Nick for a while longer.

Then they brought him to the town, and had him locked up.

Returning to the Dalton mansion, and meeting Lizzie, they told her what they discovered by pumping the negro.

She was, of course, delighted to learn that her father was alive, and was eager for the detectives to go to his rescue.

"We'll make the attempt to-morrow morning," said Harry.

"I don't see why you are putting it off so long," exclaimed the girl, petulantly. "I can get you all the help you may need."

"Let us work our own way," quietly answered the boy. "Knowing that we've captured Nick, and may have pumped him, Mason will very likely be on the lookout for us, and meet us with a hot reception. By waiting, it will lead him to think we don't know anything about his subterranean abode. Then, when we attack, we will have a better chance of taking him by surprise."

The girl pondered a moment.

Cool reflection showed her the wisdom of Harry's plan.

"You are right," she admitted, reluctantly. "I'm so anxious to have something done for my poor father's instant relief that I can hardly suppress my impatience, though."

"We understand your feelings in the matter," replied Old King Brady, quietly. "But we know best how to handle your cousin. If you will leave the matter to our judgment, we will stand a better chance of making a success of our plans."

It required no argument to convince the girl, and she sighed, and said:

"Very well, Mr. Brady. Do as you think best. All I ask is that you will not lose any time about going to my father's rescue."

They discussed the matter fully that night.

In the morning the detectives returned to the swamp.

A careful examination was made of the dreary waste of mud and water, but they failed to see any signs of their men.

It was a bright, sunny day, but a dense vapor hung over the marshy land, and the officers went through it to the island.

They expected by coming so early in the morning to catch their enemies sleeping. But a discovery Harry made dispelled this idea.

He caught view of a tiny stream of smoke rising from some rocks.

Upon examining the spot, he found a natural chimney coming up through the ground, out of which the smoke was pouring.

When he returned to his partner and told him about it, he said: