* * *

He paused and listened. From the distance came a dull drone of sound
which brought him to his feet with a start. He raced out onto deck with
Carnes at his heels. Far overhead in the blue, a tiny speck of black
hovered.

"We're on the right trail, Carnes," he said grimly. The plane passed
over them. In huge circles it sank toward the ground. Dr. Bird turned to
Captain Evans. Orders flew from the bridge and a detail of marines
rapidly stripped the covers from the two forward anti-aircraft rifles.

"I dislike to fire on that craft before it makes a hostile
demonstration, Dr. Bird," demurred Captain Evans. "We are at peace with
Russia. My action in firing might precipitate a war, or in any event,
serious diplomatic misunderstandings."

"Allow me to correct you, Captain Evans, we are at war with Russia. The
whole world is at war with the man who has pulled the earth out of her
course. In any event, your orders are positive and the responsibility is
mine. Wait until that plane gets within easy range and then shoot it
down. Do not fail to get it; it must not get back to shore with word of
our approach."

Captain Evans bowed gravely. Shells came up from the magazines and were
piled by the guns. From the fire control stations came a monotonous
calling of firing data. The guns slowly changed direction as the plane
descended. Nearer and nearer it came, intent on positive identification
of the war vessel below it. It passed over the _Denver_ less than five
thousand feet up. As it passed it swung off to one side and began to
climb sharply. Dr. Bird glanced at the fighting top of the cruiser and
swore softly. From the top the stars and stripes had been broken to the
breeze.

"Fire at once!" he cried, "and then court-martial the fool who broke out
that flag!"

* * * * *

The two three-inch rifles barked their message of death into the sky.
For agonizing seconds nothing happened. The guns roared again. Below and
behind the fleeing plane, two puffs of white smoke appeared in the sky.
The staccato calls of the observers came from the control station and
the guns roared again and again. Now above and now below the Russian
plane appeared the white puffs that told of bursting shells, but the
plane droned on, unharmed.

"It's away safely," groaned the doctor. "Now the fat _is_ in the fire.
Saranoff will know in an hour that we are coming. If we had a pursuit
plane ready to