above great stretches of barren lands. The air was biting cold. They were thankful enough for their face-protectors, their electric hand and foot warmers, their fur-lined leather union-alls. But best of all was the glorious freedom of it. Soaring on and on over untrodden wildernesses, with no thought of dangers known and unknown, made them feel like explorers of a new world. The engines worked in perfect harmony. A gentle breeze from the south urged them on their way. The sun soon set and a long night began, but what of that? The moon and snow lighted the earth as if by day, and with a silvery glory. And now the Northern Lights began to flicker, flash and shoot across the sky.

Now they passed over a wide expanse of white, which they knew to be Dismal Lake. This was frozen over; then surely Great Bear Lake, two hundred miles farther north, would be frozen, too. Their safe landing would be assured.

But as they neared their goal the boys' minds could scarcely escape misgivings. If the Major's suppositions were correct; if, indeed, this trader was the hired agent of a fanatical clan, would he not be armed and on the alert? Would he not, perhaps, have Indians and half-breeds hired to help guard his secret? They were but three. The enemy might number a score. As Barney thought of all this, he was thankful for one thing: by some strange chance, a small machine-gun and two thousand rounds of ammunition had been shipped north with the plane. Their first thought had been to leave this behind, but after a discussion, they had decided to bring it; and there it was now, hanging in its swivel before him. In an emergency there remained but to load it and go into action. But it was quite an unexpected emergency that soon made him bless that bit of equipment.

They were now well into the Arctic. The air cut like a knife and chilled them to the marrow. Barney began to long for warmth, food and sleep. He held his electric glove to the glass of the small clock before him. When the frost had thawed he noted the hour.

"Twelve o'clock! Midnight!" he muttered. "And no landing in sight yet."

There remained but to "carry on."

But what was this? Far to the North there showed a small, red ball of light. And it was not the Aurora Borealis! They were traveling fast. The ball of fire seemed to roll toward them along the earth at terrific speed, growing larger and more lurid. And now, beside it, wafting from it, like the tail to a comet, they could discern a swirling cloud, black in the moonlight.

"It's a fire!" Bruce gasped through his mouthpiece.

"But what?—" began Barney.

Just at that moment he caught the faint white line that marked the shore of Great Bear Lake. They were, then, nearing their destination. Tilting the plane upward, that they might get a better panorama of the region, and so direct their course, Barney gave the great engine more gas. On they swept. Presently the outlines of bays and frozen streams, of scrub forests and barren lands were plainly visible. A map under glass was just before him. Brushing the frost from it, Barney examined it by the light of a small electric bulb. Then he looked away at the fire which was now clearly visible. His heart sank. The trading post was, indeed, a reality, or had been. At the present moment it was a ball of fire.

"It's the trading post!" He barked to the Major.

"'Fraid so," grumbled the Major, hoarsely.

"And the gasoline for our return—"

"There it goes," sang Bruce, with a note of despair.

At that instant the whole ball of fire seemed to rise in air to burst like some gigantic rocket. There was no question in the boys' minds but that the supply of gasoline had been reached by the flames.

After the great flash came blackness. The fire seemed for a time to have been extinguished. Gradually here and there, far below, bits of burning tinder gleamed, fiery stars in an inverted heaven. Soon the ruins were again blazing. They soared close, but high, avoiding the dangerous pockets of smoke gas. Did they see dark figures dancing about the ruins? Or was it merely the flickering shadows of posts and tree stumps.

"Indians!" murmured Barney.

Instantly his mind mirrored to him pictures he had seen in histories of painted savages burning a settler's cabin. His blood ran cold. Here they were, three men in the frozen wilderness, with little gasoline for their machine, with scant provisions and ammunition, and rushing toward perils they could not even guess. To kill and to escape would both be easy for these desperadoes.

"Go along down the lake and back again. Use as little gas as possible, but keep in the air. We better not land at present." The very steadiness of the Major's tone told Barney that this experienced man of the North expected the worst.

As they rushed down the white expanse, many thoughts raced through Barney's mind. It seemed that hunger and cold grew upon him with every whirl of the engine-shaft. He thought of Bruce and La Vaune. Would they ever return to La Vaune with the money which was rightfully hers? And Timmie? Would they ever be able to help him blot the stain from his name? Barney's friend, Dave Tower, who had gone North in a submarine on a mission as mysterious as their own; would they ever meet?

They had now turned and were making their way slowly back. The fire had burned down to a dull red glow. The forest about had escaped the flames, and this was fortunate. Should the Indians leave them unmolested, they might possibly find a means of sustaining life by hunting and trapping.

"When we get to the bay, might as well land," grumbled the Major. "It's mighty tough up here!"

Barney assured him that it certainly was tough. He was glad they were to land, being very sure that if an Indian did shoot him he would not feel it, so thoroughly benumbed was he with cold.

Then, suddenly, he gave a cry of surprise. They were nearing a point where Conjurer's Bay should appear. Instead of the bay he saw what appeared to be merely a broad shoulder of frozen water, and beyond that, perhaps two miles, was a small lake lined by the forest. It was on the edge of this small lake that the fire smouldered. The boy rubbed his eyes, then looked again. Had the cold benumbed his senses? Was he seeing things? Was he asleep and dreaming?

Apparently not, for from Bruce through the receiver came a groan, then;

"What's happened? The whole shape of the lake has changed within an hour!"

Barney shut off the engines. In the welcome silence which followed, as they drifted downward in a slow spiral, not a man spoke. Their eyes were focused upon the earth.

But now there came to their ears a sound like the distant rush of many waters. This grew rapidly louder, and finally divided itself into rattling and snapping sounds.

Presently the Major let out a roar of laughter.

"Caribou!" he exploded. "They pass south from the barren lands in herds of hundreds of thousands, so thick they look like land! Tip her nose up for another circle. See! There is the end of the herd away there in the distance. We'll be able to land where they have passed in fifteen minutes, an ideal landing-place—tramped hard."

With a grin Barney obeyed orders, and, as his engines began to revolve, felt himself shooting skyward.

"Now it's clear," roared the Major.

Barney did not respond on the instant. He was thinking of something he had read about the "camp-followers of the barren-ground caribou." A chill not of the wind and cold crept into his heart. But what was to be done? He felt that another hour aloft would so