Dorothy reached beneath her seat, brought forth a pair of field-glasses and clapped them to her goggles. Focussed through the powerful lenses, there was no mistaking the Mystery Plane. And although at this distance it was impossible to see the pilot’s face, she could plainly distinguish the barrel of a machine gun that poked its wicked muzzle over the cockpit’s cowling.

“So the bearded aviator means mischief!” She returned the glasses to their case. “That guy must be a cold-blooded dog to try anything like that over a populated township. He’s likely to bite off more than he can chew if Bill and I have any luck. If he cracks up, I shan’t weep.”

At first sight of the smuggler’s plane, she brought Will-o’-the-Wisp back on an even keel, but now in order to get an unimpeded view directly below, she sent the plane into a steep bank.

Bill, in the Ryan, with an altitude of some twenty-five hundred feet and its nose slightly raised was streaking toward the smuggler.

Most air battles are fought in the higher ether, because combat flying often necessitates acrobatics and the ordinary pilot wants plenty of air below for such work. The smuggler being the aggressor in this case, naturally started to climb when he spotted the Ryan. He hoped, no doubt, not only to increase his altitude but to gain greater ascendency over Bill before diving at the monoplane with his machine gun going full blast.

It was time for Dorothy to act. As the smuggler’s plane began to ascend, she sent her amphibian diving toward him at a tremendous spurt of speed. The Mystery Plane nosed over and dove in turn at the Ryan, some five hundred feet below.

“Ha-ha!” Dorothy shut off her motor and brought Will-o’-the-Wisp’s nose gradually back to the horizontal. “Our scheme worked! That bird either doesn’t know his business or he’s lost his nerve!”

A fighting plane attacking has as its objective a position directly behind the hostile plane at close range. A position either above or below the tail is equally good. From these positions the enemy is directly in the line of fire, and in sighting no deflection is necessary.

The smuggler’s maneuver showed Dorothy that he was a novice; for instead of going into a climbing spiral which would have eluded her dive and made it possible for him to attain a superior position over both planes, he dove at the Ryan. This might have been a proper fighting maneuver if Bill’s plane had not been nosing upward toward him; and had the Ryan not been the faster of the two.

By this blunder he put himself in the direct line of fire from Bill’s machine gun. And had that young man been minded to use it the battle would have been over—almost before it started.

Seeing his mistake almost immediately, the bearded aviator broke his dive by zooming upward. Again Dorothy’s plane dove for his tail and right there he made his second error.

Instead of gaining altitude and position by making an Immelman turn, which consists of a half-roll on the top of a loop, he pulled back his stick sharply, simultaneously giving the Mystery Plane full right rudder. The result was an abrupt stall and a fall off, and his amphibian emerged from the resultant dive headed in the direction from which he had first appeared.

Dorothy sent her bus spiralling downward, while Bill simply nosed his Ryan into a steeper climb. By the time the Mystery Plane levelled off from its split-S turn it had lost over a thousand feet. Granted he was headed for home, if that had been his intention; now he was placed in the worst possible situation with regard to his opponents. For instead of one, both planes had attained positions above him.

For the next few minutes the man in the smuggler’s plane did his best to out-maneuver the elusive pair whose motors roared above his head like giant bees attacking an enemy. Never was he given a chance to better his position or to gain altitude. Every time he maneuvered to place one of the planes within line of fire from his machine gun, the other would effectually block the move; the menacing plane would sheer off at a tangent and its partner, crowding down upon his tail, would hurl forth a smoke bomb. By the time he floundered through the cloud, his antagonists would be back in their relative positions, again, the one directly above his tail plane, the other slightly behind him to the right.

The bearded aviator knew that he was being outclassed at every move, that gradually they were forcing him down to a point where he must land or crash.

Both Dorothy and Bill knew exactly when the man in the plane below guessed their purpose. For with a sudden burst of speed he shot ahead, streaking in the direction of North Stamford like a ghost in torment.

“We’ve got every advantage but one,” mused Dorothy, widening her throttle in pursuit. “He knows where he’s going—and we don’t. He’s up to some trick, I’ll bet.”

That her thoughts were prophetic was made apparent almost immediately. By shutting off his engine and by kicking his rudder alternately right and left with comparatively slow and heavy movements, the smuggler pilot sent his plane’s nose swinging from side to side. This evolution, known as fish-tailing, he executed without banking or dropping the nose to a steeper angle. Its purpose is to cut down speed and to do so as rapidly as possible.

The Mystery Plane slowed down as though a brake had been applied, sideslipped to the left over a line of trees and leveled off above a field enclosed by a dilapidated stone fence.

“Confound!” exclaimed Dorothy, with a glance behind. “He’s going to land and both Bill and I have overshot the field!”

Nose depressed below level, a lively flipper turn to left brought Will-o’-the-Wisp sharply round facing the field again with its wings almost vertical. Immediate application of up aileron and opposite rudder quickly brought the amphibian to an even keel once more. Then Dorothy nosed over, went into a forward slip, recovered and leveled off for a landing.

As the wheels of her plane touched the ground, she saw the Ryan come to a stop on the grass some yards to the right. Just ahead and between them was the Mystery Plane. It lay drunkenly over on one side, resting on its twisted landing gear and a crumpled lower wing section.

Dorothy stood up in her cockpit when Will-o’-the-Wisp stopped rolling and saw the smuggler-pilot vault the wall at the far corner of the field and disappear into a small wood. Bill was walking toward the disabled amphibian. She got out of her plane and hurried toward him.

“Pancaked!” she cried, pointing toward the wreck as she came within speaking distance.

“You said it—” concurred Bill. “That guy was in such a hurry he leveled off too soon. Usually I don’t wish anybody hard luck but that bird is the great exception. Too bad he didn’t break a leg along with his plane. Now he’s beat it and—”

“We are just about where we were before,” she broke in.

“Not quite, Dorothy. The Mystery Plane is out of commission.—I wonder where we are?”

“Somewhere in the North Stamford hills.”

“I know—but whose property are we on?”

“Haven’t the least idea.”

“I can’t see any houses around here. Did you notice any as you came down?”

Dorothy shook her head and laughed.

“My eyes were glued on this field,” she admitted. “I was too busy trying to make a landing myself to take in much of the landscape. Wait a minute, though—seems to me I caught a glimpse of the Castle just before I put Wispy into that reverse control turn. Yes, I’m sure of it.”

“The Castle?” Bill frowned. “What in the cock-eyed world is that?”

“A castle, silly!”

“Make sense out of that, please.”

“Sorry. You’re usually trying to mystify me—I just thought I’d turn the tables for a change.”

“Oh, I know—I’ll say I’m sorry or anything else you want. Only please tell me what you’re talking about.”

“Well, it seems that about fifteen or sixteen years ago, somebody built a castle about two or three miles from North Stamford village. It’s less than five miles from where we live. Not being up on medieval architecture I can’t describe it properly, but Dad says it is the kind that German robber barons put up in the fourteenth century. Anyway, the Castle is built of stone with a steep, slate roof, which spouts pointed turrets all over the place. I wouldn’t be surprised if it had been built by a German—it certainly looks as Heinie as sauerkraut!”

“Who lives there?” asked Bill.

“Nobody, now. During the war, Dad told me, the place was suspected to be a spy-hang-out or something like that. Anyway, there was a lot of talk about it. What became of the owner, whoever he is, I don’t know. The place has been rented several times during the past few years. It is quite near the road. I drove past it just the other day on my way to and from Nance Wilkins’ tea and the old dump looked quite empty and forlorn.”

“Well, that’s that,” said Bill. “This bearded guy may have been heading for your Castle, but I doubt it. Fact is, he probably decided to land at the first convenient place when he found we were too much for him, and decided to trust to his legs for a getaway.”

Dorothy had been swinging her helmet by its chin strap in an absent-minded manner. Now she raised her eyes to his.

“What are we going to do about it?” she inquired. “We can’t try to break into the Castle in broad daylight.”

“Hardly. And after our experience with the bank gang, we’ll do no more snooping around strange houses on our own. I am going over to that little wood where our friend ran to cover. Maybe I can find some trace of him. You stay here with the planes.”

“Why can’t I go with you, Bill?”

“Because that smuggler may simply be hiding in the woods in hopes that we’ll come after him and that we’ll leave these airbuses unguarded. Then when we’re gone, he’ll come back here, grab one of them and fly quietly home.”

“All right. I see.”

“Have you got a gun?”

“That small Colt you gave me is in Wispy’s cockpit.”

“Get it and keep it on you—and if that guy shows up, don’t be afraid to use it.”

Dorothy shook her head. “I never shot at anybody in my life—”

“Don’t shoot at him—shoot him. You might have to, you know.”

“But surely, Bill—”

“Oh, I don’t mean for you to kill the guy. Plunk him in the leg—disable him. If you have any qualms about it, just remember that machine gun in his bus here. The man is as deadly as a copperhead and twice as treacherous. Look out for him.”

“I will. But su-suppose you get into trouble, Bill. How long do you want me to wait here before I come after you?”

“My dear girl,” Bill was becoming impatient. “I’m just going to try to find out where that lad is headed. I won’t be gone more than ten or fifteen minutes.”

“Yes. But suppose you don’t come back here!”

“Wait for half an hour. Then fly back home and tell Dad what has happened. He’ll know what to do. Don’t get nervous—I’ll be all right. So long. See you in a few minutes.”

With a wave of his hand, he ran across the field and Dorothy saw him hurdle the low wall and disappear between the trees of the wood where the bearded aviator had run to cover.