The four children made their way to the high rocky ledge. Andy made them lie down flat and wriggle like Red Indians as they reached it.
"Better not let ourselves be seen, if anyone is down there," he whispered. So, as flat as snakes, they wormed their way to the rocky ledge—and when they got there, they had the biggest surprise of their lives!
In the quiet water that lay outside the second island was a large and powerful seaplane!
Yes—a great seaplane, whose wings spread widely over the blue water. No small motor-boat purred there. It was the seaplane's engine that Andy had heard so mysteriously in the middle of the night.
"Whew! Look at that!" whispered Andy, his face going as red as a beetroot with excitement. "I never thought of a seaplane! What a very extraordinary thing!"
"Let's get up and shout and wave." begged Jill. "I'm sure they will love to rescue us."
"Haven't you seen the sign on the wings?" asked Tom, in a curiously angry voice. The girls looked. The sign of the crooked cross was painted on each wing—the sign of the enemy, the foe of half the world.
"Golly!" said Mary, and she drew a deep breath. "Enemies I Using these islands! Do they belong to them?"
"Of course not," said Andy. "But they are desolate, and out of the usual ships' course—and they've been noted by the enemy, and he's using them as a kind of base for something—seaplanes perhaps."
"Well—what are we going to do?" asked Tom.
"We shall have to think," said Andy. "One thing is certain. We won't show ourselves tell we've found out a fitted more. We don't want to be taken prisoner."
"That's what that food was for, then—the people who come here," said Jill. "I suppose the seaplanes come over here for food and petrol. Ifs a good idea. How I wish we could get away and tell my father about it—he'd know what to do. I guess he'd clean up this place, whatever it's used for!"
"I say—hadn't we better take down our signal whilst that seaplane is here?" asked Jill. "If it happens to see it, the enemy will know there are people on this island". And" what about the fishing-boat? That might be seen too."
"I don't think so," said Andy. "It's well hidden between those rocks. But the signal had certainly better come down. We won't put it up any more. Come on. Tom—we'll take it down now."
"We'll come with you," said the girls. But Andy shook his head.
"No," he said "From now oh, somebody must keep a watch on that seaplane. We must find out all we can. We will be back with you as soon as possible—but you must stay here and watch."
So the two girls were left behind whilst the boys ran across the island to take down their flapping signal.
"I don't know where in the world we should hide if we were discovered and hunted for," said Andy, rolling up the sail. "There isn't a single place here to hide away in—not a cave or anything."
Tom felt rather uncomfortable. He didn't want to be hunted for on that bare island! "I wish we could see how many men there are in that seaplane," he said, "and what they are doing, and everything."
"Where are your field-glasses?" asked Andy suddenly. "They would be just the thing to use. We could see everything as dearly as could be, then!"
"And my camera, too!" said Tom, jumping for joy. "What about my camera? We could take some photographs of the seaplane—then everyone would have to believe us when we get back—if ever we do get back!"
"That's a fine idea!" said Andy, really pleased. "Golly! If we could take some pictures of that seaplane with the crooked cross showing up clearly, there wouldn't be the least doubt of our story when we got home. Tom, let's go and get your glasses and your camera straight away."
They dumped the sail into a bush and ran to the shack. They took Tom's field-glasses and picked up the camera to see if it needed a new film. No—there was a new one inside.
"Better not use up all the film on the seaplane," said Andy. "There might be other interesting and extraordinary things to photograph—you never know!"
"Oh, I've got three or four films," said Tom. "I brought plenty with me, thinking I was going to get some good bird pictures, you know. Come on-let's go back to the girls and see what they have to report."
The girls were very glad indeed to see the boys. They had a lot to tell.
"Andy! Tom! As soon as you had gone the men in the seaplane put out a funny little round sort of boat," said Jill in excitement. "And they paddled to shore in it, and went to our cave. What a good thing the sea had washed away all our footprints!"
"It was, indeed," said Andy. "Tom, give me the field-glasses. I want to have a look through them."
Andy stared through the powerful glasses. They were so strong that they seemed to bring the seaplane near enough to touch! The boy saw the great crooked crosses boldly painted on the wings. He saw the little rubber boat left bobbing in the surf, whilst the men visited the cave—either to take something to it, or to bring something away, Andy did not know which.
"There seems to be someone in the seaplane," said Andy. "And, look—there are some men coming from the cave!"
Andy could see them very clearly through his field-glasses—and the others could see them too, though not so well, of course. To them the men looked like faraway dolls.
"They've gone to get food from the cave," said Andy in excitement. "And I guess there's a store of petrol somewhere else for them to get when they want to. Food—and petrol—just what I thought! Using these islands saves enemy planes from having to go hundreds of miles to their own country's stores. My word—we have stumbled on to something queer!"
The men entered their rubber boat and rowed back to the seaplane. Twice more they went to the cave and back. Then they climbed up into the plane and disappeared.
"I'm getting most awfully hungry," said Tom at last. "Can't we go and get something to eat?"
"I'll stay here and keep watch, and you and the girls can go and get your dinner," said Andy. "Don't light a fire, whatever you do—the enemy will see the smoke. Use the stove if you want to cook anything. Bring me something to eat and drink later."
"Right," said Tom, and he and the girls wriggled off the high ledge. They stood upright as soon as they were out of sight of the seaplane and tore to their shack.
They ate a hurried meal, and did not cook anything at all. They made up a dinner-packet for Andy and set off to take it to him.
But half-way there they heard a noise. R-r-r-r-r-r-r-r-r! R-r-r-r-r-r-r-r! R-r-r-r-r-r-r! They stopped at once and listened.
"It's the seaplane going off!" cried Tom—and then the sound came again, more loudly than ever. R-R-R-R-R-R-R.
"Look—it's there!" cried Jill. "Drop flat to the ground or we'll be seen!"
Jill had seen the seaplane just rising into the air over the cliff. The three children dropped flat to the ground and lay there perfectly still. The seaplane roared over their island, rose higher and higher, and at last was nothing but a speck in the sky.
"What a narrow escape!" said Tom, sitting up and wiping his forehead. "Golly! My heart did go bump I I've split the water I was carrying for Andy. I'll have to get some more!"
"It was a shock to see that enormous plane coming!" said Jill. "Oh dear—if we have many more shocks, my hair will turn grey!"
"Andy, do you think there's anything to be seen over on the other islands?" asked Tom.
"There may be," said Andy, "I think we ought to try and find out. That third island looks a peculiar shape to me—very long indeed, but very narrow. On the other side of it might be a fine natural harbour for seaplanes. There may be heaps there."
"Well, we've only heard one so far," said Tom. "It doesn't seem as if they're very busy, if there are lots over there."
"No—you're right, Tom," said Andy. "Well, what about going to see what we can find? I don't quite know how we'll get to the third island—have to swim. I think. I don't believe the girls could swim so far, though."
"I don't think I could," said Jill, remembering the long stretch of sea between the second and third islands. "You boys would have to go without us. Mary and I will stay behind and be as patient as we can."
"Shall we go to-morrow?" asked Tom eagerly. "We could cross to the second island at low tide in the morning and swim across to the third island. We could carry a little food with us, wrapped up in your oilskin."
"Yes—we'lldo mat," said Andy. A great feeling of excitement came over the children—a feeling as if some big unknown secret was going to be theirs. Jill shivered a little—it was almost too exciting.
"There's one thing I'm worried about" said Andy. "Just suppose we are discovered, by any chance—we must find some hiding-place."
"Well, there simply isn't any on this island," said Tom. "So we must hope we won't be discovered."
Nothing more happened that day. No seaplane came to the calm harbour in the waters of the second island. No sound but the sea-gulls came through the air. It was a lovely day and the children enjoyed themselves bathing and sunning their brown bodies.
Thanks to the store of food they had discovered on the second island they had plenty to eat. Andy caught some nice little fish, and Jill fried them in tine tinned butter. They were delicious. Now that they had tinned mule-powder they could make a milk-mixture and use it with their tea or cocoa, and could also sweeten their drinks with the sugar they had brought.
"We are really very well off now!" said Tom, who as usual was thoroughly enjoying his meal. "we'll take another exciting lot of tins away from the Round Cave next time—I saw some baked beans in tomato sauce. I should like those."
The children took turns at keeping watch on the second island from the rocky ledge. But nothing was to be seen at all. They went to bed early because the boys would have rather a hard and long day the next day.
"We shall have to clamber over that line of rocks first," said Andy. "And then we must cross the island and swim to the third one. We shall have to be back on the second island in time to clamber over the rocks at the next low tide. You girls mustn't worry about us. We shall be back all right."
"I do wish we were going too," said Jill. "Don't you think Mary and I could climb over the rocks to the second island and wait for you there? It would be more fun for us to play about there than on this bare island. There are lots of bilberries there we could pick—they are lovely and sweet now."
"All right," said Andy. "But just keep a watch for any seaplane arriving. Lie down fiat under a bush or something if you hear one. You mustn't be seen."
"All right," said Mary. "You can trust us to do that."
So the next morning the four children once again climbed over the line of slippery rocks at low tide. The boys had on only their bathing-suits. Andy had tied his oilskin packet safely to his shoulders, and in it was plenty of food for the day. The girls could get what they wanted from the cave.
All four went across the second island, over the heather and bracken to where they could see the third island. It lay in the sea before them, like a long blue and brown snake. Beyond they could see one or two more islands.
"Do you really think you can swan so far, Tom?" asked Mary doubtfully, as she looked at the wide spread of water between the second island and the third.
"Of course," said Tom, who wasn't going to give up this adventure for anything. All the same, the distance was further than he had ever swum before.
"Well—good-bye for the present," said Andy to the girls. "We'll get down to the shore here, wade out as far as we can, and then swim. Have you got Tom? field-glasses, Jill? Good—you can watch us through them all the way to the third island!"
The boys went down to the shore, waded into the water, and then, when they were out of their depth, began to swim. Andy was by far the stronger swimmer—but he kept close to Tom, just in case the younger boy got into difficulties.
On and on they swam, using the breast-stroke because Andy said it was the least tiring. When Tom began to pant a little, half-way across, Andy spoke to him.
"Let's do a spot of floating, Tom. That will rest us a little. It's a long way."
The two boys lay on their backs in the water. It was a little rough and choppy, but quite warm. They floated like logs of wood, spread out flat on the water. It was a fine rest for Tom.
Then once more they swam on—but it began to seem as if Tom would not reach the shore of the third island. His arms felt so tired. His legs seemed to have no push in them. He gasped and panted, and Andy began to feel alarmed.
"Tread water a bit," he called to Tom. "Do you think you'll be able to swim the rest of the way?"
"I don't know," said poor Tom, dreadfully ashamed of himself. But he could not seem to make his arms work properly. He was really tired out.
Andy was not in the least tired. He was as strong as a horse, and he trod water beside Tom, wondering what to do.
"Try again, Tom," he said. "It's no use going back! We are more than half-way across."
Tom looked at the cliff of the third island. It seemed a long, long way away still. He tried again, striking out bravely with his tired arms. But after about six strokes he could not swim any more. He turned on his back and floated again.
Andy was really alarmed. "Tom, you can't do any more," he said. "I'D have to help you. I'll swim on my beak and you must lie on your front and put your hands on my shoulders. I can drag you along in the water that way, but it will be rather slow."
"Thanks, Andy," said Tom, very angry with his poor swimming, but quite unable to do anything else. He took hold of Andy's shoulders, and Andy, lying on his back with his head towards the third island, began to strike out valiantly with his brown legs.
It was very slow indeed. And now Andy began to get tired! Taking two people wasn't nearly so easy as only one, and he began to gasp. Now what were they to do? If they both got into difficulties it would be a very serious matter.
It wasn't long before neither Tom nor Andy had any strength left—and goodness knows what would have happened if Andy, striking out desperately with his legs, had not fit something hard beneath him. It was a rock! He felt about with his feet and at last discovered a rock below the water. They had come to a kind of rocky reef rather like the one they had climbed over from their own island to the second one—but this line of rocks was not uncovered by the tide.
"Tom! Tom! Put your feet down and feel where the rocks are!" gasped Andy. "We can stand there—and maybe feel our way along a bit till we come to the sandy bottom."