“We can’t do any signalling till to-morrow,” said Jack. “What a pity! All the letters are ready!”

Again the next day the children kept a three-hourly watch, and about two o’clock in the afternoon Jack and Nora saw the boy prisoner. He came to the window and leaned out as far as he could.

“He’s looking down into the grounds to make sure that nobody can see him waving to us,” said Jack. “Sensible fellow!”

Jack waved from his window, and the boy saw him and waved back. “Now we’ll do a bit of letter-work!” said Jack excitedly. “Give me the letters I want, Nora, please, and I’ll send him a message. I hope he can read!”

“What message are you sending?” asked Nora.

“Well. I think I’ll just say ‘WE ARE FRIENDS,’ ” said Jack. “Hand me the letters one by one.”

So Nora handed Jack the big letters drawn in black on the white paper. First a big W, then a big E, and so on. The boy prisoner watched the letters eagerly.

He read the words as the letters made them and nodded his head and smiled and waved. Then he began making letters with his fingers - but Jack could not see them so far away. He snatched up the field-glasses and looked through them. The boy began his message again. He held up one finger first.

“That’s ‘I,’ ” said Jack. Then the boy slanted his two first fingers together and crossed them with a middle finger.

“That’s ‘A,’ ” said Jack. Then the boy turned his hands the other way and made the letter M with four fingers.

“ ‘M’! ” said Jack. “ ‘I AM’ he has spelt out so far, Nora.”

The boy went on making the letters very cleverly with his fingers - and he spelt out the message “I AM A PRISONER.”

By this time Mike and Peggy had come upstairs to get their bathing-suits, which they had forgotten - but when they saw what was going on they sat down excitedly on Mike’s bed, whilst Jack spelt out the prisoner’s message.

“Jack, ask him who he is!” cried Nora, dancing up and down in excitement. So Jack spelt out the question with his black letters. And, dear me, what a surprising answer he got!

Jack had been watching the boy’s answer through the field-glasses. The others sat near him, waiting eagerly to know who the boy was. They could see him making letters with his fingers, but they could not see what letters they were for, unlike Jack, they had no glasses to help them.

“Who is he, Jack? Who is the prisoner?” cried Nora impatiently.

“Well,” said Jack, turning to them, “he has just spelt out in his fingers that he is Prince Paul!”

The others stared at him in surprise.

“Prince Paul!” said Peggy. “A prince! What country is he prince of?”

“I don’t know,” said Jack. “I’ll ask him. Where are the letters?”

But by the time he had got the first one, Prince Paul had disappeared. He went quite suddenly, as if someone had pulled him back. Jack darted back from his own window, and pulled Peggy with him. They almost fell on the floor and Peggy was quite cross.

“Don’t, Jack,” she began - but then she saw Jack’s face, and she followed his eyes, and saw what he saw. Mr. Diaz and sleepy-eyed Luiz were both at the far tower window - and they were looking very hard indeed at the children’s window.

“Did he see us, Jack?” said Peggy, speaking in a whisper, as if she was afraid that Mr. Diaz might hear her.

“No,” said Jack. “We got away just in time. Maybe they went into the prisoner’s room and caught him signalling. Or maybe they just took him away from the window because they wanted to look out themselves. I’m sure they know this is our bedroom!”

“Jack, do you think we can possibly rescue that boy?” asked Nora eagerly. “And do you think he really is a prince?”

“We can’t rescue him by using the secret passage,” said Jack, “because even if we used it, it only takes us to the cellars, and Mr. Diaz keeps the tower-room locked. This is going to be difficult.”

“We shall have to be very careful not to be seen by Mr. Diaz at our window,” said Nora. “Perhaps he already thinks we know about the prisoner.”

“He can’t know that,” said Jack. “He didn’t see our messages.”

“I say! I’ve got an idea!” said Mike. “What about us making a rope-ladder and getting up to the tower-room on it at night?”

“But how could we get it up to the window?” said Nora.

“Well, if we can tell the prisoner about it he can help to pull it up,” said Jack. “You know how to get a rope-ladder up to a high window, don’t you? First of all you tie a stone or something heavy on to a long piece of string. Then you tie the piece of string on to a thin twine. Then you tie the twine to the rope-ladder. You throw the stone up to the window and the person there catches it, pulls up the string. Pulls up the twine - and the rope-ladder comes last of all! He fixes it safely to something and escapes!”

“That’s a grand idea!” said the others.

“Let’s try it,” said Peggy.

“We’ll have to get string and twine and rope,” said Nora.

“George will let us have some,” said Mike.

“Let’s go and ask him now!” said Jack, jumping up. So down the stairs they rushed and out into the field where they knew George was working that day.

“George, George! Can you let us have lots of string and twine and rope?” yelled Jack.

“I dare say,” said George. “What do you want it for?”

“It’s a secret,” said Mike. “We’ll tell you later on.”

“You can go to my old boat in the cove and open the locker there,” said George. “There’s a mighty lot of string and stuff all tangled up there. You can have the loan of it if you want it.”

“Oh, thank you, George!” cried the four children, and they tore off to the cove. They found George’s boat and opened the locker at one end of it. Sure enough there was a mighty lot of string and twine and rope there, that George used for mending and making fishing-nets.

“Goodness! It’ll take some time to untangle all this!” said Peggy.

“Well, there’s four of us to do it,” said Jack. “We might as well sit here in the boat and get on with it now.”

“What shall we make the rungs of the ladder with?” said Peggy.

“There’s some little wooden stakes, quite strong, in Dimmy’s garden shed,” said Jack. “I saw them there the other day. They would be the very thing!”

“Look! Look!” said Peggy suddenly, in a low voice. The others looked up, and saw, coming across the sand towards them, the yellow-haired woman who had been with Mr. Diaz in the car, and who lived at the Old House.

“That must be Mrs. Diaz,” said Nora. “Is she coming to talk to us, I wonder?”

“Leave me to do the talking,” said Jack. “She’s been sent to find out how much we know, I’m sure.”

Mrs. Diaz came slowly over to them, holding a big sunshade over her head. She nodded to the children.

“You are very busy,” she said. “What are you doing?”

“Oh, playing about in George’s boat,” said Jack.

“You are often on the beach?” asked the woman, putting down her sunshade. “You play all the time here?”

“Nearly all,” said Jack. “We can’t when the tide is in.”

“Have you seen these exciting caves?” asked Mrs. Diaz, pointing to the caves with her sunshade. “Have you ever been in any, I wonder?”

“We don’t like them because they are dark and damp,” said Jack.

“Have none of the other children any tongues?” asked Mrs. Diaz, in a slightly sharp voice.

“They’re rather shy,” said Jack. “I’m their captain, anyway, so I do the talking.”

“Oh,” said Mrs. Diaz. She made a pattern in the sand with her sunshade point. “How long are you staying at Peep-Hole?” she asked.

“Oh, not long,” said Jack.

“Your bedrooms are in the tower, aren’t they?” asked Mrs. Diaz, looking straight at Jack. Jack looked straight back.

“Yes,” he said. “They are.”

“Can you see the Old House from your bedrooms?” asked the golden-haired woman.