"I certainly am sorry we don't have Susie with us," remarked Dot, as the girls sat down to their late dinner that evening, after their refreshing swim. "I thought she'd be better than a 'talkie' for amusement."

"Yes, you would have enjoyed her, Dot," agreed Linda, picking up the menu and studying it with a great deal of interest. "I'm going to order everything here, Dot. I'm simply starved."

"So am I, though I ought to be ashamed to admit it. You should have seen the lunch I ate!"

"And you should have seen my lunch!" returned Linda. "We forgot to carry anything, but fortunately Susie had left beans and coffee on the island."

"Is that all you had?"

Linda nodded, and gave her order to the waiter.

"I'd certainly like to know where Susie is now," she remarked, after she had satisfied the sharpest pangs of hunger with an iced fruit-cup.

"Yes, so would I," agreed Dot. "Her disappearance will make it a lot harder to trace that other thief.... Do you really expect to do anything about hunting him, Linda?"

"Indeed I do! Tomorrow's only the twenty-seventh, and I don't have to report to Atlanta until July first. I'm going to use those four days."

"But what could you possibly do?" inquired Dot. "How would you know where to go—without even a suggestion from Susie?"

"I have a theory," explained the other girl. "Wait till I eat some of this beef-steak, and I'll tell you about it."

"I'm crazy to hear it, because I'll be with you all the time. Mother said I must start back home the first of July—the day you go to Atlanta. I have my ticket bought."

For a few moments Linda ate her dinner in silence, enjoying every mouthful as only a hungry person can. Then, lowering her voice so that there was no danger of being overheard, she told her chum her plan.

"I've thought it all out," she began. "This is what must have happened: That thief—the 'Doc,' as the gang called him—took the boat and the money the day after the bank robbery, when he woke up and found that Susie and her husband had flown away in the autogiro, and the other two were still asleep. His idea was to get out of the swamp to the St. Mary's or some other river, that would take him to the ocean."

"And get on a steamer?" demanded Dot. "But Linda, if he did that, he's out of the country by now."

"I'm not so sure of that. A canoe trip like that would take a good while—the Okefenokee is fifty miles at least from the coast. And he'd be afraid to take a train—or an automobile, for fear of being seen. Besides, I don't think he'd take a steamer right away. He'd want to go to that island first."

"In his canoe?" inquired the other, skeptically.

"No, of course not. He'd hire a motor-boat—or steal one."

"I still don't understand why he'd want to get to that island," remarked Dot.

"For two reasons," explained Linda. "One because he expected to pick up those jewels—which we have already taken away—and the other reason is that the gang has arrangements with some party that owns a steamer, to stop at the island on certain specified dates. That would be his way of getting out of the country."

"It does sound plausible," admitted Dot. "What a brain you have, Linda!"

"Not a bit of that, Dot! It's only that I've been so closely associated with these criminals that I'm beginning to see their motives."

"And where does Susie come into all this?"

"The man must have seen her on Soldiers' Camp Island, from his canoe. Or rather, he saw the wrecked autogiro, and knew she must be there."

"And forced her to go with him?"

"Probably. He didn't want to take any chances, leaving her free to help the police."

Linda paused for a moment to eat the salad with which she had been served, and glanced about the dining-room. No one seemed to know her, or notice her—for that she was sincerely thankful.

It was not until they had finished their dinner and found a cool, secluded spot on the veranda, that she went on with her plan.

"What I mean to do," she said quietly, "is to fly back to the camp on Black Jack Island early tomorrow. Not that I expect to find anyone there—but merely to get my direction—to go on to that island in the ocean. I don't know its name, so I couldn't look it up on the map."

"You really expect to catch those two on that island?" asked Dot, excitedly. "Will you take the police along?"

"No! I don't want to tell them a word about all this, except to say that I am going scouting about the country, and to ask for a couple of revolvers.... And, in answer to your first question, I don't really expect to find Susie and the 'Doc' there yet. But I believe they'll be along soon."

"And we wait for them there?"

"Yes. Take them unawares. Susie will probably be on our side, and we can plan something with her.... Of course this is all only theory. Maybe there isn't a thing in it. That gang was slick; they seemed to know how to drop right off the face of the earth. And I believe this man may be the cleverest of them all. He was quiet; it's the boasting kind, like Susie's husband, who usually get caught first.... So you can see why I don't want any of the police along."

"We better take plenty of food, though," remarked Dot.

"We will take some—but don't forget that we can easily fly back to the coast each night. The island is only a few miles out—it's nothing in a plane."

"True," admitted the other.

"And we'll keep our room here at the hotel, for we want some place as headquarters. We'll put a few over-night necessities into my bag."

"O.K. I'll order a roast chicken and a chocolate cake from the dining-room tonight."

"Oranges, too," added Linda. "They always taste so good. I mustn't forget to fill my thermos-bottles, either."

They went to bed early that night, in order to get a good start on the following morning. Dot, who was particularly enthusiastic about the chocolate cake, carried the basket of food, while Linda took the handbag. They arrived at the City Hall immediately after breakfast, and were ushered right into Captain Magee's office.

"No news of the fourth man yet," he said, after he had greeted Linda and been introduced to Dot. "But I've sent out a call for him by radio, so that all ships are to be warned to be on the look-out for a fellow of his description."

"There's something else I want to tell you," added Linda, "that may help to spot him. There is probably a girl with him." Then, rather reluctantly, she told what she knew of Susie, begging the Captain not to punish her too severely if she were found.

"And now," she concluded, "Miss Crowley and I want to do a little scouting ourselves—in the autogiro—and I want to know whether you will lend us a couple of .38s for the undertaking."

The Captain smiled whimsically. What an unusual girl Linda Carlton was! No wonder she had done things no other girl had even tried.

"Of course I will," he said. "Though such a request is rather out of the ordinary——"

"This is an extraordinary occasion," remarked Linda.

"Don't you want a detective to go with you?" he asked.

"No, thank you, we haven't room in the autogiro. Besides, we don't want to waste his time—for it may be only a wild goose chase. But if you will lend us a couple of revolvers, I think we shall be safe."

"Can you shoot?"

"If it is necessary. But I don't think it will be. The girl got to be very friendly with me, after her husband was killed. If I had only gotten to her in time, I think I could have saved her. As it is, she may not have joined the man of her own free will. You see she had been hurt, and was partially helpless. So he could do most anything he liked with her, if he had her alone."

"Well, good luck to you!" said the Captain. "I certainly take off my hat to a plucky pair of girls."

When Linda and Dot arrived at the airport they found the Ladybug in readiness for its second flight into the swamp. Linda inspected her, and piled in the equipment.

"I feel as if the Okefenokee Swamp were my home," she remarked, as she headed the autogiro in that direction. "I could almost fly it blind!"

"Don't!" warned Dot. "Your friend the Doc is still at large, and he may be watching for us with a gun."

This was Dot's first view of the swamp, and as they approached it, she was amazed at the vast expanse of it, stretching out in every direction.

"It's huge, isn't it?" she shouted to Linda, through the speaking-tube.

"Forty miles long and thirty wide," was the reply. "But we see only the southern end of it."

Conversation was difficult, so the girls gave it up until they came to Black Jack Island, where Linda had been held a prisoner.

"Shall we get out?" she asked her companion. "Or go straight on to the ocean?"

"Let's get out," replied Dot. "They might possibly be here, you know. Besides, I'm crazy to see their camp."

Linda brought the autogiro to earth and the girls climbed out cautiously, their revolvers in readiness, lest the enemy appear. But there was no human sound—nothing but the birds and the insects.

"Watch out for snakes, Dot!" warned Linda. "I'd almost rather meet the Doc than a snake, I believe."

They walked carefully towards the camp only to find it absolutely deserted.

"Let's look all around," suggested Linda, who remembered everything only too well. "We'll begin with the mess-tent."

Quietly at first, they snooped around, peering into boxes of provisions, looking under the cots, behind the tents, and, when they were quite sure that they were alone, they began to act more natural, to laugh and joke with each other.

Linda showed Dot the tent which she had shared with Susie that one night of her captivity, and they both smiled over the sight of the magazine which had led to Linda's escape.

"We could even stay here all night if we had to," Dot remarked. "Seems comfortable enough."

Linda shuddered.

"Never again!" she protested. "But we may as well eat some lunch before we fly to that island. I'm hungry."

"And thirsty. But it isn't so hot here as it was in Jacksonville."

"No. And the island out in the ocean ought to be cooler yet. You may like it so well that you'll want to spend the summer there. Only it has no tents or cots, like this camp."

"Thank you, I'd rather not play Robinson Crusoe," replied Dot.

"Poor man!" sighed Linda. "If he'd only had an airplane, how simple it would have been for him."

They ate their lunch, and then, for the third time, Linda flew across the Okefenokee and over the coastal plain of Georgia—out to the barren island in the ocean where the treasure had been hidden. The desolate loneliness of the spot impressed her companion.

"You suggested this as a summer resort!" she remarked, when they had landed. "Why, I don't even see a fishing-boat!"

"That's just the trouble," replied Linda. "The first time I flew here—with Susie's husband—I looked about desperately for somebody to shout to for help. And there wasn't a soul! Nothing but ocean and sky.... Do you have your revolver handy, Dot?"

"Yes. Right here. But I don't know much about shooting."

"I'm sure we shan't have to. I just want to explore. But 'be prepared' is our motto."

"I will be. I won't shoot you, either, Linda—you can count on me for that."

Climbing out of the autogiro they walked towards the center of the island where the sand was soft and the underbrush thick. Perhaps, thought Linda, there might be more hiding places than the one hole which she knew; it would be worth while to make a thorough search. On and on they plodded, the sand sinking into their shoes, the sun beating down upon them with full blast, for what trees there were, were not high enough to afford much shade. It was difficult to find the hiding place in such monotonous desolation, but at last she came to the spot.

"Somebody's been here since I came with the police!" she said to Dot, "because we left the stones as we found them. But it looks as if the hole is empty."

She was correct in her surmise. After five minutes of pushing the sand away, Linda had assured herself that nothing was there.

"Let's go down to the opposite shore from the one we came in on," suggested Dot. "And explore that."

"All right," agreed Linda. "If you can stand walking through this sand again...." She stopped abruptly, peering towards the shore. An instant later she dragged the other girl to the ground. "The Doc!" she whispered, hoarsely. "I saw him down by the water—maybe there's a boat coming!"

"What shall we do?" demanded Dot, clutching her revolver tightly.

"Wait till he gets on—and follow in the autogiro. I've got plenty of gas.... Let's be creeping back to the Ladybug."

The girls kept well hidden behind the underbrush, crawling along on their hands and knees. Suddenly Dot stopped; she had struck something solid. A canvas bag—two bags, stuffed full with something. Could it be the money?

Breathless, they both stopped while Linda untwisted with her pen-knife the coarse pieces of wire around the tops of the bags, and dumped out the contents. Money in an amount they had never seen before! Hundred dollar bills in rolls that they had no time to count, bonds in thousand-dollar denominations!

"Hide it quickly, Dot!" whispered Linda. "In your pockets, your riding-breeches—stuff some of it in my clothes—while I re-fill these bags with sand.... And have your revolver ready."