"Let's don't say anything about our little mishap," whispered Linda, as the flying couple got out of their plane. "For one thing, I'd just as soon not boast about stunts in front of Aunt Emily. She would be worried all the more."

"And I'm not any too proud of the fact that I was so careless about a valuable necklace," returned Ralph. "So we'll keep it our secret."

There was no time for further words. Everybody rushed at them, shouting joyous welcomes. Louise was the first to kiss Linda—then all the others, and finally her aunt.

"Thank Heaven you're safe!" cried the latter. "I couldn't eat a bite of lunch, I was so uneasy."

"Of course we're safe," assured Ralph. "And maybe if we'd come by motor, we should have had an accident. There was a big smash-up—two automobiles—outside of Spring City this morning."

"Isn't the air up here wonderful!" exclaimed Miss Carlton. "After that stuffy town of ours!"

"I think the airport is wonderful," replied Linda, "for so small a place. But as for the air—well, don't forget Auntie dear, that Ralph and I have been having marvelous air—up in the skies!"

"Hope you didn't give him the air," remarked Maurice Stetson, solemnly.

Kitty Clavering gave the young man a withering look, and inquired of the flyers when they might hope for rides. "Oh, I don't mean today," she added, "for I know you must both be nearly dead."

"Not a bit of it!" denied Linda, who still looked as fresh as a flower in her becoming blue and white suit. "But it's supposed to be wise to have a mechanic go over your plane each time you fly. Just a precaution, you see."

"A very good rule to follow," commented Miss Carlton. "Now everybody get into their cars, and we'll go over to our bungalow for some ginger-ale and sandwiches."

"Just a moment, please!" interrupted a voice at her elbow, and everyone turned to see a newspaper man with a camera. "Pictures, please!"

Linda and Ralph smilingly agreed, and their friends stepped aside. Then they all piled into the three machines that were waiting for them; while the strangers who had been watching commented on the beautiful biplane, and the handsome couple who had been flying it, and wondered whether they were married.

"Did you bring my necklace, Ralph?" asked Kitty Clavering, as he got into her roadster with her and Maurice.

"Surest thing!" he replied, as if nothing at all had happened on the way. Reaching into his pocket, he pulled out the pasteboard box, with the French jeweler's name engraved on the lid.

"Thanks a lot," she replied. "Maurry, you take care of it till we get home, so long as you're sitting in the middle. Mind you don't lose it! I think as much of that as Linda does of her plane."

"But not as much of it as you do of me?" asked the youth, flippantly.

"A thousand times more! Like the old question people always ask married men: 'If your mother and your wife were drowning, which one would you save?' Well, if you and the necklace were drowning, I'd go after my necklace!"

"Righto. Necklaces, no matter how valuable, have never been known to swim. I do."

It was only a five minute ride from the airport to Miss Carlton's bungalow, so Kitty waited until they had all gone inside the pleasant living-room to open her box, and gaze at her beloved treasure once more.

"I'm dying to see it again," she said, as she took the box from Maurice's hand. "If I had my way, I wouldn't keep it in a safe-deposit vault. I like it where I can look at it."

She took off the rubber bands and opened the box, displaying the velvet case inside. But when she unfastened the clasp, her expression of delight changed abruptly to one of horror. The case was empty!

Her exclamation of distress was pitiful to hear. Her dearest possession—gone!

"Ralph!" she cried with torturing accusation. "Ralph! Are you teasing me?"

Her brother's face became ghastly white.

"What—what's wrong—Kit?" he stammered.

"My necklace! Oh, what has happened?" She burst out crying.

Everybody crowded around and gazed in consternation at the empty box, looking questioningly at Ralph, to see whether it could possibly be intended as a joke. But he did not need to tell them of his innocence; he looked almost as stricken as his sister. He knew now that it had been stolen by the man who pretended to be a pilot! And he had actually made twenty dollars out of Ralph besides, for the transaction! What fools they had been, never to open the box!

"It's all my fault!" cried Linda, contritely. "My silly, foolish, childishness, for wanting to show off!"

Nobody of course had any idea what she was talking about—nobody except Ralph.

"No! No! It was mine!" he protested. "My carelessness!"

"Then you both knew!" exclaimed Kitty, raising her head, which she had buried on Linda's shoulder while she sobbed. "Oh, how cruel, not to prepare me!"

"On my honor, we didn't!" averred Ralph, and from the look on his face, his sister knew that he was telling the truth.

"Explain what you meant, then," she commanded.

"Let me tell you," put in Linda. "But sit down, Kit dear. You're liable to faint.... You see, we were robbed, and too foolish to suspect it. We even paid the robber twenty dollars for doing the job."

"So you said," Kitty remarked, impatiently. "Do you mean that you saw somebody take it—right under your eyes?" She had dropped down on the couch, and her pale little face was pitiful to see. The tears still ran down her cheeks, washing tiny rivers through the powder. Luckily she was not a girl who used rouge, or she would have looked ridiculous. As it was, she gave the appearance of a very unhappy child.

"Exactly!" explained Linda. "Or rather, we might have, if we had had sense enough to realize it. I wanted to try a couple of loops, and we started quite high, but by the time we had finished, we were over an open field. It was then that Ralph suddenly realized that the box had dropped out of his pocket when the plane was on its side. So we decided to land, and search the field."

"And somebody had already picked it up?" demanded Dot, excitedly.

"No. Another airplane—I had noticed it before—landed soon after we came down. The pilot walked over and asked us if we were in trouble."

"And you stupids told him all about the fifty-thousand-dollar necklace!" cried Louise, in disgust.

"No, we didn't! We were smart enough to know that wouldn't be wise. We thought we knew him, though—we had seen him at the Spring City Flying School. But we did tell him we had lost a necklace, and he said he had picked something up. As a matter of fact, we had noticed him stoop over."

"And you took it and thanked him, and never looked inside!" cried Kitty.

"I'm afraid you're right," admitted Ralph. "We thought he was a friend, following us for our protection, at the orders of the school."

"Well, then, why was he following you?" demanded Kitty, incredulously.

"He must have overheard us talking about the necklace," answered Linda slowly, for she was trying to think the thing out. "Yes—that is what I believe he was doing all the time, Ralph. Now I remember—the day we got our licenses!"

"You mean you went around the school shouting the news that you were carrying pearls to Green Falls in an airplane?" asked the unhappy girl.

"Of course not! Only the men at the bank—the safe-deposit vault—really knew about it. And of course they're absolutely trustworthy! Except maybe this one man—who was fixing his car outside the aviation field. We never thought he was listening—why we couldn't even see him!"

"Children," interrupted Miss Carlton, who had been patiently waiting to serve the refreshments, "wouldn't you all feel better if you ate something? Then we can discuss what are the best steps to take to capture the thief."

They agreed, but Linda and Ralph and Kitty were all extremely nervous; they hated to lose any time. Ralph decided to telephone to a lawyer at once in Spring City, to put expert detectives on the job, and to get in touch with the Flying School.

"Lucky the necklace was insured," remarked Maurice Stetson, as he drank his ginger-ale.

"Yes, but Dad will never get me another!" moaned Kitty, disconsolately. "He'll say I was careless, and invest the insurance in bonds, to be kept in trust till I'm older—or something like that." She started to cry afresh. "And I only wore the necklace twice—at graduation and at the class dance!"

Linda watched her sorrow with more than sympathy—with remorse. It was her fault, she was sure! Of course she couldn't imagine caring so much for a pearl necklace, when such lovely imitations were made, but it wasn't her place to judge. Kitty probably wouldn't understand why she loved her Arrow so much.

Slowly, painfully, she came to her decision. She rose and went over to the couch where Kitty was sitting, and crowded in between the latter and Dot.

"It's my fault, Kit," she said, "and of course I can't pay for it—but I can help. I'm—I'm—going to sell my airplane, and—give you the money. Then you can start buying a new one—a couple of pearls at a time."

Kitty squeezed her hand affectionately.

"You're a dear, Linda, but I couldn't possibly let you do that. Besides, it was really Ralph's fault."

"Of course it was!" put in the young man, returning from making his telephone call. "But we're going to catch that thief!" he announced, with conviction. "I've just been talking with Lieutenant Kingsberry at the field, and he says that fellow didn't even have a license, that they only took him on temporarily, as sort of errand boy. And he deliberately stole that plane!"

"I thought he was about the poorest pilot I ever saw!" cried Linda, jumping up excitedly at this piece of news. "He'll probably crash, sooner or later.... Ralph!" Her eyes were shining with inspiration.... "Let's go out after him—ourselves!"

"Lieutenant Kingsberry is broadcasting the news all over—to all the airports," replied the young man. "Everybody will be watching for him. Do you think there would be any use in our going?"

"Yes! Yes! We might be just the ones to spot him! Oh, come on!"

"But haven't you had enough flying for today, Linda?" inquired Miss Carlton, anxiously.

"We won't go far, Auntie dear," answered the girl. "Just around to the nearest airports, and see if anybody has any information. The practice of landing and taking-off again will be good for us both.... And you needn't worry one bit!... Now, who'll drive us over to our 'Pursuit'?"

"'Pursuit' is right," remarked Maurice. "Your plane has the right name, Linda!"

Louise immediately offered her services, and in less than five minutes the young pilots had washed their faces and were ready to start. Ten minutes later they climbed into the cockpit on the runway of the airport, and, this time with Ralph at the controls, they took off for the nearest airport.

Ralph was delighted to be piloting a plane again, and in his enthusiasm he almost forgot the seriousness of his mission. A king of the air, he thought, and his lips were smiling. But Linda could not forget so easily.

Like most young men, he loved going fast, and as soon as he was high enough, he let the plane out to her maximum speed. Over the clouds they sailed, at a rate of seventy miles an hour, yet they did not seem to be traveling fast. Linda had no sense of danger, yet it was the first flight she had ever made that she did not thoroughly enjoy, for, unlike Ralph, she could not for one moment forget Kitty's tragedy.

Twenty minutes, however, was all that was needed to reach their first port, and Ralph, not quite so skilled or so careful as Linda, made, nevertheless a pretty landing. It was a large field, evidently designed for amateur sport flyers, and there were a number of licensed mechanics in readiness to greet new arrivals.

Ralph lost no time in telling his story to the first man who came forward. Had they any information so far? he inquired.

"Only of a wreck about fifteen miles away," replied the latter. "That may be your man—if, as you say, he is not an experienced pilot."

"Can you give us directions?" put in Linda excitedly.

"Certainly," replied the other, taking a map from his pocket, and indicating the position of the wreck. "We've already sent a doctor and a nurse—and telephoned for an ambulance." Marking the spot, he handed the map to Ralph.

Jumping into the plane at once, Linda took control, for she felt surer of herself than of her companion in an emergency. The boy was so absent-minded, so likely to forget things in his excitement.

Their destination was a field again, but not a large one, this time, and already a small crowd, gathered from passing automobiles, had collected. Here landing was not so easy as in the airports designed for that very purpose. But the girl knew just what she was doing, and she handled the situation with a dexterity that would have brought credit to a far more experienced pilot.

Over against an embankment, its wings smashed to pieces, a plane was lying on its side, mutely testifying to the truth of the mechanic's statement.

"There's the wreck!" cried Ralph, as he and Linda stepped on the ground. "Do you think it's the Waco?"

Grabbing her companion's arm, Linda ran forward eagerly. When they were within fifty yards of it, she knew that it was the very plane they were seeking.

"It is! Oh, Ralph! Even the license number—so I'm sure! Remember? Look! Do you suppose that man was killed?"

"Would serve him right!" muttered the boy, resentfully. "Stealing a necklace, and crashing a plane that wasn't his! But let's go over and have a peep at him—there's the ambulance."

The crowd, which was still gathering, although the field was in an isolated spot, was being held back by a policeman, for the ambulance was ready to start. Ralph dashed forward, anxious to get a look at the thief before it departed.

"Not that we could claim the necklace now," he explained to Linda, whose arm he was holding, "for we haven't any proofs of our ownership. But at least we could warn the cop to look out for it."

"Back! Back!" shouted the officer, for the driver was tooting his horn.

"Oh, please wait a minute!" begged Linda. "Please let me see the man who is inside!"

The policeman regarded the girl doubtfully, but she was so eager in her pleading that he thought perhaps she had a good reason. Perhaps the man inside the ambulance meant something to her; he decided to grant her request.

"Take a look, miss," he agreed. "But be quick about it."

Stepping ahead of Ralph, Linda climbed upon the back step of the car, and peered anxiously into it, past the white-clad interne, to the unconscious figure on the stretcher. Suddenly she started violently, and clung to the door of the ambulance for support. It was incredible, impossible! Her knees shook, her hands fell to her side, and she swayed backward in a faint. In an instant Ralph's arms were around her; he carried her out of the crowd.

The unconscious man in the ambulance was none other than Ted Mackay!