companion, and there was a noticeable tremor in
his voice.

They were destined to feel that earth-tremble many times before they
solved the mystery of the mine.

CHAPTER II

"FIFTEEN MEN ON THE DEAD MAN'S CHEST"

The two men who, with the young doctor, accompanied Johnny and Pant back
to the mine were old friends of other days, David Tower and Jarvis,
one-time skipper and engineer of the submarine in that remarkable race
beneath the ice and through the air told about in our second book, "Lost
in the Air." Like all worthy seamen, they had found that money "burned
holes in their pockets," and before six months had passed their share of
the prize money had dwindled to such a meager sum that the fitting out of
a private expedition to go north in search of the fabled City of Gold, the
gleam of whose domes they had glimpsed, was not to be thought of. When,
therefore, they had discovered that men were being signed for a trip to
Arctic Russia with the well-known feather-weight champion boxer, Johnny
Thompson, at its head, they hastened to put their names on the "dotted
line." And here they were, two of Johnny's most valued men.

Both worked hard at the labor entrusted to them. But ever and again, as he
straightened up to ease his cramped back, Jarvis would whisper to Dave:

"It's all right this 'ere Seven Mines, but, man, think how rich we'll be
when we git to that City of Gold. I 'ates to think how rich we'll be.
We'll buy reindeer or dogs from the bloody, bloomin' 'eathen and we'll
trim our sails for the nor'west when this hexpedition's blowed up and
gone."

Dave had always smiled and hoped.

But now, there lay before them a sad task. One of their comrades, a fine
young college fellow with all of life before him, had been "bumped off."
It was their duty to determine, if possible, who was responsible for this
tragedy, and, if occasion seemed to warrant, to avenge it.

With bowed heads, they stood beside the quiet form while the young doctor
went about his examination.

For fully ten minutes the mine was silent as a grave. Only the faint drip,
drip, drip of water from the warm spring and the almost inaudible
tremble-mumble of the throbbing earth disturbed the deathlike stillness.

At last the doctor straightened up with a sigh.

"Not a scratch on his body," he announced, "not a sign of anything."

"Heart disease?" suggested Johnny.

"Impossible. I was particularly careful to see that every man of the
e