It was sometimes difficult to remember which day it was. Jack had kept a count as best he could, and sometimes on Sundays the children could hear a church bell ringing if the wind was in the right direction.

“We ought to try and keep Sunday a day of rest and peace,” said Mike. “We can’t go to church, but we could make the day a good sort of day, if you know what I mean.”

So they kept Sunday quietly, and the little island always seemed an extra peaceful day then. They hardly ever knew what the other days were - whether it was Tuesday or Thursday or Wednesday! But Jack always told them when it was Sunday, and it was the one day they really knew. Nora said it had a different feel, and certainly the island seemed to know it was Sunday, and was a dreamier, quieter place then.

One day Jack said they must explore the caves in the hillside.

“If anyone does come here to look for us, and it’s quite likely,” he said, “we must really have all our plans made as to what to do, and know exactly where to hide. People who are really looking for us won’t just sit about on that beach as the trippers did, you know - they will hunt all over the island.”

“Well, let’s go and explore the caves to-day,” said Mike. “I’ll get the lantern.”

So, with the lantern swinging in his hand, and a box of matches ready in his pocket to light it, Jack led the way to the caves. The children had found three openings into the hillside - one where the hens had been put, another larger one, and a third very tiny one through which they could hardly crawl.

“We’ll go in through the biggest entrance,” said Jack. He lighted the lantern, and went into the dark cave. It seemed strange to leave the hot July sunshine. Nora shivered. She thought the caves were rather queer. But she didn’t say anything, only kept very close to Mike.

Jack swung the lantern round and lit up all the corners. It was a large cave - but not of much use for hiding in, for every corner could be easily seen. Big cobwebs hung here and there, and there was a musty smell of bats.

Mike went all round the walls, peeping and prying - and right at the very back of the cave he discovered a curious thing. The wall was split from about six feet downwards, and a big crack, about two feet across, yawned there. At first it seemed as if the crack simply showed rock behind it - but it didn’t. There was a narrow, winding passage there, half hidden by a jutting-out piece of rock.

“Look here!” cried Mike, in excitement. “Here’s a passage right in the very rock of the hillside itself. Come on, Jack, bring your lantern here. I wonder if it goes very far back.”

Jack lifted up his lantern and the others saw the curious half-hidden passage, the entrance to which was by the crack in the wall. Jack went through the crack and walked a little way down the passage.

“Come on!” he cried. “It’s all right! The air smells fresh here, and the passage seems to lead to somewhere.”

The children crowded after him in excitement. What an adventure this was!

The passage wound here and there, and sometimes the children had to step over rocks and piles of fallen earth. Tree-roots stretched over their heads now and again. The passage was sometimes very narrow, but quite passable. And at last it ended - and Jack found that it led to an even larger cave right in the very middle of the hill itself! He lifted his lantern and looked round. The air smelt fresh and sweet. Why was that?

“Look!” cried Nora, pointing upwards. “I can see daylight!”

Sure enough, a long way up, a spot of bright daylight came through into the dark cave. Jack was puzzled. “I think some rabbits must have burrowed into the hill, and come out unexpectedly into this cave,” he said. “And their hole is where we can see that spot of daylight. Well - the fresh air comes in, anyhow!”

From the big cave a low passage led to another cave on the right. This passage was so low that the children had to crawl through it - and to their surprise they found that this second cave led out to the hillside itself, and was no other than the cave into which it was so hard to crawl because of the small entrance.

“Well, we are getting on,” said Jack. “We have discovered that the big cave we knew leads by a passage to an even bigger one - and from that big one we can get into this smaller one, which has an opening on to the hillside - and that opening is too small for any grown-up to get into!”

“What about the cave we put the hens into?” asked Nora.

“That must be just a little separate cave by itself,” said Jack. “We’ll go and see.”

So they squeezed themselves out of the tiny entrance of the last cave, and went to the hen-cave. But this was quite ordinary - just a little low, rounded cave smelling strongly of bats.

They came out and sat on the hillside in the bright sunshine. It was lovely to sit there in the warmth after the cold, dark caves.

“Now listen,” said Jack thoughtfully. “Those caves are going to be jolly useful to us this summer if anyone comes to get us. We could get Daisy into that big inner cave quite well, for one thing.”

“Oh, Jack! She’d never squeeze through that narrow, winding passage,” said Peggy.

“Oh yes, she would,” said Jack. “She’d come with me all right - and what’s more, Daisy is going to practise going in and out there, so that if the time comes when she has really got to hide for a few hours, she won’t mind. It wouldn’t be any good putting her into that cave, and then having her moo fit to lift off the top of the hill!”

Everyone laughed. Mike nodded his head. “Quite right,” he said. “Daisy will have to practise! I suppose the hens can go there quite well, too?”

“Easily,” said Jack. “And so can we!”

“The only things we can’t take into the cave are our boat and our house,” said Mike.

“The boat would never be found under those brambles by the water,” said Jack, “And I doubt if anyone would ever find Willow House either, for we have built it in the very middle of that thicket, and it is all we can do to squeeze through to it! Grown-ups could never get through. Why, we shall soon have to climb a tree and drop down to Willow House if the bushes and trees round it grow any more thickly!”

“I almost wish someone would come!” said Peggy. “It would be so exciting to hide away!”

“A bit too exciting!” said Jack. “Remember, there’s a lot to be done as soon as we see anyone coming!”

“Hadn’t we better plan it all out now?” said Mike. “Then we shall each know what to do.”

“Yes,” said Jack. “Well, I’ll manage Daisy the cow, and go straight off to fetch her. Mike, you manage the hens and get them into a sack, and take them straight up to the cave. Peggy, you stamp out the fire and scatter the hot sticks. Also you must put out the empty cigarette packet, the tin, and the cardboard carton that the trippers left, so that it will look as if trippers have been here, and nobody will think it’s funny to find the remains of a fire, or any other odd thing.”

“And what shall I do?” asked Nora.

“You must go to the spring and take the pail of milk from there to the cave,” said Jack. “Before you do that scatter heather over our patches of growing seeds. And Peggy, you might make certain the cave-cupboard is hidden by a curtain of bracken or something.”

“Ay, ay, Captain!” said Peggy. “Now we’ve all got our duties to do - but you’ve got the hardest, Jack! I wouldn’t like to hide Daisy away down that narrow passage! What will you do if she gets stuck?”

“She won’t get stuck,” said Jack. "She’s not as fat as all that! By the way, we’d better put a cup or two in the cave, and some heather, in case we have to hide up for a good many hours. We can drink milk then, and have somewhere soft to lie on.”

“We’d better keep a candle or two in the entrance,” said Peggy. “I don’t feel like sitting in the dark there.”

“I’ll tell you what we’ll do,” said Jack thoughtfully. “We won’t go in and out of that big inner cave by the narrow passage leading from the outer cave. We’ll go in and out by that tiny cave we can hardly squeeze in by. It leads to the inner cave, as we found out. If we keep using the other cave and the passage to go in, we are sure to leave marks, and give ourselves away. I’ll have to take Daisy that way, but that can’t be helped.”