The train had disappeared in the distance.
Not far away from where the Bradys stood they saw the big box lying beside the track, turned over on its side.
They ran back and hastily examined it.
"Empty!" ejaculated Harry, in some surprise.
"What has become of the man it contained?" asked Old King Brady.
"Search. He may have fallen out."
They carefully examined the ground within a wide radius.
But they found nothing of the missing body.
"Mysterious, what became of him!" Old King Brady exclaimed.
Harry was completely at his wits' end.
"I'm afraid we are beyond our depth, Old King Brady," he remarked. "This mystery keeps growing all the time, and we can't seem to fathom it."
Just then the moon appeared again.
It showed them a river on one side and a broad expanse of gloomy swamp land on the other.
Night insects were chirping amid the weeds, and frogs were croaking dismally among the waving reeds and rushes.
Off in the centre of the swamp were some tangled trees and bushes, heaps of rocks overgrown with moss and trailing vines, and an object which had the dim outline of being an old rookery of some sort.
It was a dismal, lonesome scene.
Young King Brady moved along the edge of the boggy ground with its little pools of water, tufts of coarse grass and tracts of black, oozing mud.
An old, rotten board walk from the railroad bed to the trees, caught his view and he suddenly called to the old detective:
"I see a light among those trees. Here's a path. Let's follow it into the swamp."
"Be cautious!" warned the old detective. "If those rascals have carried the body from the box to the midst of those trees, they will be on the lookout for any possible pursuers and may give us a warm reception."
"We need not let ourselves be seen," replied the boy.
"How are you going to avoid it?"
"By creeping along the path on our hands and knees. The reeds on each side will hide our bodies from view."
"Go ahead, then."
They went down on their haunches and crept along in single file, out into the dismal swamp, and drew near the oasis.
In a few minutes they reached firm land.
From behind a clump of bushes they beheld an old wooden shanty, in the windows of which there glowed a dim light.
The detectives keenly watched it, hoping they might catch view of some human beings about the place.
At the end of quarter of an hour, they were suddenly startled by hearing a wild, piercing cry in human tones, of:
"Help! Police! Murder!"
The Bradys were intensely startled.
It was the same voice, using the very same words they had heard the night before in West Thirty-sixth street, New York!
"Good gracious! That's queer!" exclaimed Old King Brady, in tones of intense astonishment. "Did you hear it, Harry?"
The boy was thinking.
A startling idea flashed across his mind and he muttered:
"That cry was uttered by the same person we heard in New York, and I'm convinced that it was the man called Albert Reid."
"But he was murdered – "
"You only suppose so. There was circumstantial evidence that he was. But after all he may yet be alive."
This was a startling view to take of the matter.
Old King Brady shot a quick glance at Harry and exclaimed:
"You may be right. The man in the box may not have been dead after all. Perhaps he was alive, under the influence of a drug. The man who drugged us may have drugged him, too, you know.
"Hark!"
A chorus of fierce cries came from the hut.
There was the noise of a scuffle, then a voice which sounded very much like that of a negro roared in furious tones:
"Keep still, or I'll kill you!"
Old King Brady rose to his feet, very much agitated.
"I can't stand this much longer, Harry!" he muttered.
"Come on to the hut and we'll investigate the row," replied the boy.
Casting aside all caution, they rushed toward the old building.
Not half the intervening distance had been covered, when suddenly the noise ceased and the light went out.
The detectives halted.
"Were we seen?" panted Harry.
"Perhaps. Listen a moment."
They remained perfectly still and the trees cast a dark shadow over the scene which the moon could not dispel.
Five minutes passed.
Hearing and seeing nothing unusual, Harry said:
"Come on."
"Wait till I light my lantern."
"I'll stand guard with my pistol."
Old King Brady drew out a match and lit his bull's-eye.
Moving forward, they reached the hut and made a circuit of it.
The door was wide open.
They boldly entered the building.
It contained only one room, and to the amazement of the officers, it was empty.
Staring around, Old King Brady observed that there was only one door and the two windows they had been watching – one at the rear and the other at the side of the little building.
The door was at another side.
"Gone!" ejaculated the old detective.
"Where?" asked the astonished boy.
"Heaven only knows."
"Search outside."
Old King Brady dashed out the door.
He saw by the moonlight that the little island on which the hut stood was in the midst of the swamp.
If any one left it, he was bound to see them.
But not a soul met his view.
No one could leave the hut, cross the swamp and reach the mainland so quick that he could not see them escaping in such a short space of time.
Yet he failed to see any one in the swamp.
That convinced him that no one left the oasis.
And nobody was on the solid island of earth.
He could not have failed to observe them if they were there.
"What the deuce does this mean?" he gasped in bewilderment.
Then he finally returned to his partner.
"See any one?" eagerly asked the boy.
"Not a soul. And you?"
"I've searched this place, but no one is here."
"Then where did they disappear to so mysteriously?"
"Blessed if I know."
"You heard two human voices here, didn't you?"
"Of course I did."
"Have you thoroughly examined this place?"
"Every inch of it, and couldn't find them."
Old King Brady made a round of the room and came back.
He plainly saw that the walls were not double, and that the floor was merely covered with common