City of the Living Flame

The legendary city of M'Tonak lay hidden beneath Mar's Polar cap, its heart a pulsing flame from outer space. Jim Landor found the fabulous green flame, found it sentiently, evilly alive—and that its living meant death for all mankind.
Startled into action, Jim Landor straightened in his seat. He peered eagerly through the forward visiplate of the tiny rocket-plane.
From the Martian metropolis that nestled in the opposite hemisphere, thirteen hundred miles away, he had taken the poorly-mapped, wearisome, rocket-course of the Polar route in order to save time. Thus he avoided being hampered by the magnetic storms raging over the Red Desert at this season. At least, so he'd told his friends.
But the real, the all-important reason he had kept to himself. It was not only that they would have laughed at him, that mattered little; but that a growing, nameless dread made him even more reserved than usual. He smiled thinly now as he visualized their reactions had he dared mention the mythical city of M'Tonak. M'Tonak, city of forgotten men, where reposed the fabulous emerald large enough to ransom a world!
Yes, Jim thought without bitterness; at last he had joined the fatal number of men, usually Earthmen, who had searched for M'Tonak. He was persuaded against all reason that it did exist somewhere among the polar wastes, and it was most imperative that he find it! He was sure that then he would find his brother too, who had disappeared scarcely a month before. In his perilous passage above the Cap, Jim had zig-zagged the rocket-plane dangerously off its course, searching the limitless white wastes with the intentness of desperation. But in vain.
Well, he murmured now, no M'Tonak, so I'll settle for Riida—for the time being.
The tiny Martian town was beneath him, its crazy conical structures reaching up like pointing forefingers. Jim's hand came down on the descent lever. A ghostly whirr disturbed the stillness as the plane's stubby wings sliced the atmosphere on its downward glide. It contacted gently, plowing a shallow furrow in the powdery sand that rose cloud-fine to engulf him as he climbed out. Already he saw two men hurrying toward him from the town.