Water above and water around — so that was why her father had chosen Kirrin Island for his experiment. How had he found the secret passage under the sea, though? “Why, even I didn’t know of that,” said George. “Hallo — what am I coming to?”

She stopped. The passage had suddenly widened out into an enormous dark cave, whose roof was unexpectedly high, lost in dark shadows. George stared round. She saw queer things there that she didn’t understand at all — wires, glass boxes, little machines that seemed to be at work without a sound, whose centres were alive with queer, gleaming, shivering light.

Sudden sparks shot up now and again, and when that happened a funny smell crept round the cave. “How weird all this is!” thought George. “However can Father understand all these machines and things! I wonder where he is. I do hope those men haven’t made him prisoner somewhere!”

From this queer, Aladdin’s cave another tunnel led. George switched on her torch again and went into it. It was much like the other one, but the roof was higher.

She came to another cave, smaller this time, and crammed with wires of all kinds. There was a curious humming sound here, like thousands of bees in a hive. George half-expected to see some flying round.

“It must be these wires making the noise,” she said. There was nobody in the cave at all, but it led into another one, and George hoped that soon she would find Timmy and her father.

She went into the next cave, which was perfectly empty and very cold. She shivered. Then down another passage, and into a small cave. The first thing she saw beyond this tiny cave was a light!

A light! Then perhaps she was coming to the cave her father must be in! She flashed her torch round the little cave she was now standing in and saw tins of food, bottles of beer, tins of sweets, and a pile of clothes of some sort. Ah, this was where her father kept his stores. She went on to the next cave, wondering why Timmy had not heard her and come to greet her.

She looked cautiously into the cave where the light came from. Sitting at a table, his head in his hands, perfectly still, was her father! There was no sign of Timmy.

“Father!” said George. The man at the table jumped violently and turned round. He stared at George as if he really could not believe his eyes. Then he turned back again, and buried his face in his hands.

“Father!” said George again, quite frightened because he did not say anything to her.

He looked round again, and this time he got up. He stared at George once more, and then sat down heavily. George ran to him. “What’s the matter? Oh Father, what’s the matter? Where’s Timmy?”

“George! Is it really you, George? I thought I must be dreaming when I looked up and saw you!” said her father. “How did you get here? Good gracious, it’s impossible that you should be here!”