Tom leaped silently out of bed, and stood for a moment half dazed, so soundly had he been sleeping.

"Come on!" urged Ned softly, realizing that his chum had not fully comprehended. "Koku will hold them until we get there. I haven't roused anyone else."

"That's right," whispered Tom, as he began putting on his clothes. "I don't want father to know. When did it happen?"

"Just a little while ago. I couldn't sleep very well, but I fell into a doze, and then I heard the buzzer of the alarm go off. I saw that the drop, showing that the hangar had been entered, had fallen. I got to the window in time to see Koku going toward the shed from his little coop. Then I came to you."

"Glad you did," answered Tom. "I didn't think I was sleeping so soundly."

Together the two chums made their way from their rooms down the dimly-lighted hall to a side door, whence they could reach the airship hangar, or shed.

"Won't we need something--a gun or--" began Ned.

"Clubs are better--especially at night when you can't see to aim very well," whispered back Tom. "I've got a couple of good ones downstairs. I could use my electric rifle, and set it merely to disable temporarily whoever the charge hit, but it's a little too risky. Koku has a habit of getting in the way at the most unexpected times. He's so big, you know. I think clubs will be best."

"All right, Tom, just as you say," agreed Ned. "But who do you think it can be?"

"I haven't the least idea. Probably the same fellows who were after me before, though. This time I'll find out what their game is, and what they're after."

The chums reached the lower hall, and there Tom picked out two African war clubs which he had brought back with him from one of his many trips into wild lands.

"These are just the thing!" exclaimed Ned, swinging his about.

"Careful," cautioned Tom, "If you hit something you'll rouse the house, and I don't want my father and Mrs. Baggert, to say nothing of Eradicate, awakened."

"Excuse me," murmured Ned. "But we'd better be getting a move on."

"That's right," agreed Tom. He dropped into a side pocket a small but powerful electric flash lamp, and then he and Ned let themselves out.

There had been a bright moon, but it was now overcast by clouds. However, there was sufficient light to enable the two lads to see objects quite clearly. All about them were the various buildings that made up the manufacturing and experimental plant of Tom Swift and his father. Farthest away from the house was the big shed where once Tom had kept a balloon, but which was now given over to his several airships. In front of it was a big, level grassy space, needed to enable the aircraft to get a "running start" before they could mount into the clouds.

"See anything of Koku?" whispered Ned.

"No," answered Tom, in the same cautious voice. "I guess he must be hiding--"

"There he goes now!" hissed Ned, pointing to a big figure that was approaching the hangar. It was undoubtedly that of the giant, and he could be seen, in the dim light, stalking cautiously along.

"I wonder where the uninvited guests are?" asked Tom.

"Probably in the airship shed," answered Ned. "Koku was after them as soon as the alarm went off, and they couldn't have gotten away. They must be inside there yet. But what can their game be?"

"It's hard to say," admitted Tom. "They may be trying to get something belonging to me, or they may imagine they can pick up some valuable secrets. Or they may--" He stopped suddenly, and then exclaimed:

"Come on, Ned! They're after one of the airships! That's it! My big biplane is all ready to start, and they can get it in motion inside of a few seconds. Oh, why didn't I hurry?" he added, bitterly.

But the hangar was still some distance away, and it would take two or three minutes of running to reach it.

Meanwhile, and at the instant Tom had his thought of the possible theft of his biggest aircraft, something happened.

The doors of the shed were suddenly thrown open, and the two boys could see the large airship being wheeled out. The hazy light of the moon behind the clouds shone on the expanse of white planes, and on the fish-tail rudder, one of Tom's latest ideas.

"Hey, there!" cried Tom, warningly.

"Leave that alone!" yelled Ned.

"Koku! Koku!" shouted Tom, shrilly. "Get after those fellows!"

"Me get!" boomed out the giant, in his deep voice.

He had been standing near the entrance to the hangar, probably waiting for developments, and watching for the arrival of Tom and Ned. The big form was seen to leap forward, and then several dark shadows swarmed from around the airship, and were seen to fling themselves upon the giant.

"That's a fight!" cried Ned. "They're attacking him!"

"Koku can take care of himself!" murmured Tom. "But come on. I don't see what their game is."

He understood a moment later, however, for while several of the midnight visitors were engaged in a hand-to-hand tussle with the giant there came a sharp, throbbing roar of the airship motor in motion. The propellers were being whirled rapidly about.

"Koku! Koku!" cried Tom, for he was still some distance off. "Never mind them! Don't let the airship be taken!"

But Koku could only grunt. Big and strong as he was, half a dozen men attacking him at once hampered him. He threw them from him, one after another, and was gradually making his way toward the now slowly-moving airship. But would he be in time?

Tom and Ned could not hope to reach the machine before Koku, though they were running at top speed.

"Koku! Koku!" yelled Tom. "Don't let them get away!"

But Koku could only grunt--harder this time--for he fell heavily, being tripped by a stick thrust between his legs. He lay for a moment stunned.

"They're going to get away!" panted Tom, making an effort to increase his speed.

"That's what!" agreed Ned.

Even as they spoke the roar of the airship motor increased. Several of the dark forms which had been engaged in the struggle with Koku were seen to pick themselves up, and run toward the airship, that was now in motion, moving on the bicycle wheels over the grass plot, preparatory to mounting upward in the sky.

"Stop! Stop!" commanded Tom. But it was all in vain.

The men leaped aboard the airship, which could carry six persons, and a moment later, with a deafening roar, as the engine opened up full, the big craft shot upward, taking away all but two of the midnight visitors. These, who had seemingly been stunned by Koku, now arose from the ground, and staggered off in the darkness.

"Get them!" cried Tom.

"We must see to Koku!" added Ned, "Look, there goes your airship, Tom!"

"Yes, I know. But we can't stop that now. Let's see if we can get a clue in these fellows!"

He pointed toward the two who had run off in the dark underbrush surrounding the hangar plaza, and he and Ned trailed them as well as they could. But from the first they knew it would be useless, for there were many hiding places, and, a little way beyond, was a clump of trees.

After a short search Tom gave up reluctantly, and came back to where Koku was now sitting on the ground.

"Are you hurt?" he asked of the giant.

"My mind hurt--that all," said the big man.

"I guess he means his feelings are hurt," Tom explained. "Do you know who they were, Koku?"

"No, master."

"But we must do something!" cried Ned. "They've got your airship, Tom."

"I know it," said the young inventor, calmly. "But we can't do anything now. You can hardly hear her, let alone see her. She's moving fast!"

He pointed upward to the darkness. Like some black bird of prey the airship was already lost to sight, though it would have seemed as if her white planes might render her visible. But she had moved so swiftly that, during the short search, she had already disappeared.

"Aren't you going to do anything?" asked Ned.

"Certainly," spoke Tom. "I'm going to telephone an alarm to all the nearby towns. This is certainly a queer game, Ned."