“But Aunt Fanny where is he?” said Anne, with a puzzled face. “We’ve looked simply everywhere?”

Her aunt did not know the island as well as the children did. She imagined that there were plenty of places to shelter in, or to work in. “Never mind,” she said, looking quite undisturbed. “He’ll turn up later. You come along and have your meal.”

“We think we’ll go up the tower,” said Julian. “Just in case he’s up there working.”

The four children and Timmy went to where the tower rose up from the castle yard. They ran their hands over the smooth, shining sections, which were fitted together in curving rows. “What’s this stuff it’s built of?” said Dick.

“Some kind of new plastic material, I should think,” said Julian. “Very light and strong, and easily put together.”

“I should be afraid it would blow down in a gale,” said George.

“Yes, so should I,” said Dick. “Look — here is the door.”

The door was small, and rounded at the top. A key was in the keyhole. Julian turned it and unlocked the door. It opened outwards not inwards. Julian put his head inside and looked round.

There was not much room in the tower. A spiral staircase, made of the same shiny stuff as the tower itself, wound up and up and up. There was a space at one side of it, into which projected curious hook-like objects made of what looked like steel. Wire ran from one to the other.

“Better not touch them,” said Julian, looking curiously at them. “Goodness, this is like a tower out of a fairy-tale. Come on — I’m going up the stairs to the top.”

He began to climb the steep, spiral stairway. It made him quite giddy to go up and round, up and round so many, many times.

The others followed him. Tiny, slit-like windows, set sideways not downwards, were let into the side of the tower here and there, and gave a little light to the stairway. Julian looked through one, and had a wonderful view of the sea and the mainland.

He went on up to the top. When he got there he found himself in a small round room, whose sides were of thick, gleaming glass. Wires ran right into the glass itself, and then pierced through it, the free ends waving and glittering in the strong wind that blew round the tower.

There was nothing in the little room at all! Certainly Uncle Quentin was not there. It was clearly only a tower meant to take the wires up on the hook-like things, and to run them through the strange, thick glass at the top, and set them free in the air. What for? Were they catching some kind of wireless waves? Was it to do with Radar? Julian wondered, frowning, what was the meaning of the tower and the thin, shining wires?

The others crowded into the little room. Timmy came too, having managed the spiral stairs with difficulty.