Presently from the air overhead, and slightly behind them, the boys heard the sound of another motor.  They turned quickly.

“Look!” cried Ned.  “Another airship, by all that’s wonderful!”

“If we could only stop them!” exclaimed Tom.  “That’s a big machine, and they could take us aboard.  Then we could chase the Eagle.  We could catch her, too, for she’s overloaded!”

Frantically he and Tom waved their caps at the man who was now almost overhead in his airship.  The boys did not call.  They well knew, with the noise of the motor, the occupant of the airship could not hear them.  But they waved and pointed to the slowly-moving Eagle.

To their surprise and delight the man above them shut off his engine, and seemed about to come down.  Then Tom cried, knowing he could be heard: 

“Help us capture that airship?  It’s mine and they’ve stolen it!”

“All right!  Be with you in a minute!” came back the answer from above.

The second biplane came down to earth, ands as it ceased running along on its bicycle wheels, the occupant jumped out.

“Hello, Tom Swift!” he called, as he took off his goggles.

“Why—­why it’s Mr. Halling!” cried the young inventor, in delight, recognizing the birdman who had brought him the first news of Mr. Damon’s trouble, the day the airship became entangled in the aerials of the wireless on Tom’s house.

“What are you doing here, Tom?” asked Mr. Hailing.  “What has happened?”

“We’re looking for Mr. Damon.  That’s a bad crowd there,” and he pointed toward the other aircraft.  “They have my Eagle.  Can you help me catch them?”

“I certainly can—­and will!  Get aboard!  I can carry four.”

“Then you have a new machine?”

“Yes, and a dandy!  All the latest improvements—­self-starter and all!  I’m glad of a chance to show it to you.”

“And I’m glad, too!” cried Tom.  “It was providential that you happened along.  What were you doing here?”

“Just out on a trial spin.  But come on, if we’re going to catch those fellows!”

Quickly Tom, Ned, and Mr. Halling climbed into the seats of the new airship.  It was started from a switch, and in a few seconds it was on the wing, chasing after the Eagle.

Then began a strange race, a race in the air after the unknown strangers who had Tom’s machine.  Had the Eagle not been so heavily laden it might have escaped, for Tom’s craft was a speedy one.  But this time it had to give the palm to Mr. Grant Halling’s.  Faster and faster in pursuit flew the Star, as the new craft was called.  Faster and faster, until at last, coming directly over the Eagle, Mr. Halling sent his craft down in such a manner as to “blanket” the other.  In an instant she began to sink, and with cries of alarm the men shut off the motor and started to volplane to the earth.

But they made an unskillful landing.  The Eagle tilted to one side, and came down with a crash.  There were cries of pain, then silence, and a few seconds later two men ran away from the disabled airship.  But there were three senseless forms on the ground beside the craft when Tom, Ned and Mr. Halling ran up.  In the fading light Tom saw a face he knew—­three faces in fact.