“It’s — it’s a dog whining,” said Dick, suddenly.

It was. It was Timmy in the truck with George. He had heard the voices of the boys he knew, and he wanted to get to them. But George, not sure yet that the men had gone, still had her hand on his collar. Her heart beat for joy to think she was alone no longer. The three boys — and Anne, too, perhaps — were there, in the same queer place as she and Timmy were.

The boys listened hard. The whining came again. Then, George let go her hold of Timmy’s collar, and he leapt headlong out of the truck. His feet pattered eagerly over the ground. He went straight to the boys in the darkness, and Julian felt a wet tongue licking his face. A warm body pressed against him, and a little bark told him who it was.

“Timmy! I say, Dick — it’s Timmy!” cried Julian, in joy. “Where did he come from? Timmy, is it really you?”

“Woof,” said Timmy, and licked Dick next and then Jock.

“Where’s George then?” wondered Dick.

“Here,” said a voice, and out of the truck scrambled George, switching on her torch as she did so. She went over to the boys. “Whatever’s happened? How did you come here? Were you captured or something!”

“Yes,” said Julian. “But, George — where are we? And what are you doing here too? It’s like a peculiar dream!”

“I’ll cut your ropes first, before I stop to explain anything,” said George, and she took out her sharp knife. In a few moments she had cut the boys’ bonds, and they all sat up, rubbing their sore ankles and wrists, groaning.

“Thanks, George! Now I feel fine,” said Julian, getting up. “Where are we? Gracious, is that an engine there? What’s it doing here?”

“That, Julian, is the spook-train!” said George, with a laugh. “Yes, it is, really.”

“But we walked all the way down the tunnel and out of the other end, without finding it,” said Julian, puzzled. “It’s most mysterious.”

“Listen, Ju,” said George. “You know where that second tunnel is bricked up, don’t you? Well, there’s a way in through the wall — a whole bit of it moves back in a sort of open-sesame manner! The spook-train can run in through the hole, on the rails. Once it’s beyond the wall it stops, and the hole is closed up again.”

George switched her torch round to show the astonished boys the wall through which they had come. Then she swung her torch to the big wall opposite. “See that?” she said. “There are two walls across this second tunnel, with a big space in between — where the spook-train hides! Clever, isn’t it?”

“It would be, if I could see any sense in it,” said Julian. “But I can’t. Why should anyone mess about with a silly spook-train at night?”

“That’s what we’ve got to find out,” said George. “And now’s our chance. Look, Julian — look at all the caves stretching out on either side of the tunnel here. They would make wonderful hiding-places!”