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.