houted to Carnes. "We'll be safely out of
range in a minute."

* * * * *

The bursts were mostly behind them now. Suddenly a blast of air struck
them with terrific force. Half a dozen holes appeared in the fabric of
the wings. A bit of high explosive shell plowed a way through the after
compartment and wrecked the duplicate instrument board. In another
moment they were out of range. Lieutenant McCready turned the nose of
his plane toward the north.

"We came out of that well," cried Carnes. Dr. Bird dropped the speaking
tube which he had held pressed to his ear and smiled grimly at the
detective.

"I wish we had," he replied. "Our main gas tank is punctured."

An expression of alarm crossed the detective's face.

"Is it injured badly?" he asked.

"I don't know yet. McCready says that the gauge is dropping pretty
rapidly. I'm going to go out and see what I can do."

"Can't I go, Doctor? I'm a good deal lighter than you are."

"You're not as strong or as agile, Carnes, and you haven't the
mechanical ability to make the repair. Hand me that line."

He fastened one end of a coil of manila rope which Carnes handed him to
his waist, while the detective fastened the other end to one of the
safety belt hooks. With a word of farewell, he climbed out of the
cockpit and onto a wing. In the pocket of his flying suit he carried a
tool kit and repair material. Carnes shuddered as the doctor's figure
disappeared under the plane. He snubbed the rope about a seat bracket
and held it taut. For ten minutes the strain continued. It slackened at
last, and the figure of the doctor reappeared on the wing. Slowly he
climbed into the cockpit.

"I've made a temporary repair, Lieutenant," he called into the speaking
tube, "and the leakage has stopped. How much gas have we left?"

"Enough for about an hour of flying, including the emergency tank."

"Thunder! No chance to get back to the _Denver_. Better head inland and
follow the course of the Dwina. If we can locate the place we are
looking for we may be able to drop a few eggs on it before we are washed
out. In any event, it will be better to come down on land than on
water."

* * * * *

McCready headed the plane south and followed the winding ribbon below
him which marked the channel of the Dwina. He kept his altitude well
over eight thousand feet. For a few minutes the plane roared along.
Without warning the motor