“No one is down there,” said Julian. “We need not even bother to pull up the stone and go down to see. If it had been lifted lately, those weeds would have been torn up as it was raised.”

“And anyway, we know that no one can get out of the dungeon once the entrance stone is closing it,” said Dick. “It’s too heavy. Uncle Quentin wouldn’t be silly enough to shut himself in! He’d leave it open.”

“Of course he would,” said Anne. “Well — he’s not there, then. He must be somewhere else.”

“But where?” said George. “This is only a small island, and we know every corner of it. Oh — would he be in that cave we hid in once? The only cave on the island.”

“Oh yes — he might be,” said Julian. “But I doubt it. I can’t see Uncle Quentin dropping down through the hole in the cave’s roof — and that’s the only way of getting into it unless you’re going to clamber and slide about the rocks on the shore for ages. I can’t see him doing that, either.”

They made their way beyond the castle to the other side of the island. Here there was a cave they had once lived in. It could be entered with difficulty on the seaward side, as Julian had said, by clambering over slippery rocks, or it could be entered by dropping down a rope through a hole in the roof to the floor some way below.

They found the hole, half hidden in old heather. Julian felt about. The rope was still there. “I’ll slide down and have a look,” he said.

He went down the rope. It was knotted at intervals so that his feet found holding-places and he did not slide down too quickly and scorch his hands.

He was soon in the cave. A dim light came in from the seaward side. Julian took a quick look round. There was absolutely nothing there at all, except for an old box that they must have left behind when they were last here themselves.

He climbed up the rope again, his head appearing suddenly out of the hole. Dick gave him a hand.

“Well?” he said. “Any sign of Uncle Quentin?”

“No,” said Julian. “He’s not there, and hasn’t been there either, I should think. It’s a mystery! Where is he, and if he’s really doing important work where is all his stuff? I mean, we know that plenty of stuff was brought here, because Aunt Fanny told us so.”

“Do you think he’s in the tower?” said Anne, suddenly. “He might be in that glass room at the top.”

“Well, he’d see us at once, if he were!” said Julian, scornfully. “And hear our yells too! Still, we might as well have a look.”

So back to the castle they went and walked to the queer tower. Their aunt saw them and called to them. “Your lunch is ready. Come and have it. Your uncle will turn up, I expect.”