Now they were in the curious place between the two walls which were built right across the place where the second tunnel forked from the first one. The place where the spook-train stood in silence — the place where George was, still hidden in one of the trucks with Timmy! But nobody knew that, of course; not even Mr. Andrews guessed that a girl and a dog were listening in a truck nearby!

He put on a torch and flashed it in the faces of the three boys, who, although they were not showing any fear, felt rather scared all the same. This was so weird and unexpected, and they had no idea where they were at all.

“You were warned not to go down to that yard,” said the voice of one of the men. “You were told it was a bad and dangerous place. So it is. And you’ve got to suffer for not taking heed of the warning! You’ll be tied up and left here till we’ve finished our business. Maybe that’ll be three days, maybe it’ll be three weeks!”

“Look here — you can’t keep us prisoner for all that time!” said Julian, alarmed. “Why, there will be search parties out for us all over the place! They will be sure to find us.”

“Oh, no they won’t,” said the voice. “Nobody will find you here. Now, Peters — tie ’em up!”

Peters tied the three boys up. They had their legs tied, and their arms too, and were set down roughly against a wall. Julian protested again.

“What are you doing this for? We’re quite harmless. We don’t know a thing about your business, whatever it is.”

“We’re not taking any chances,” said the voice. It was not Mr. Andrews’s voice, but a firm, strong one, full of determination and a large amount of annoyance.

“What about Mum?” said Jock suddenly, to his stepfather. “She’ll be worried.”

“Well, let her be worried,” said the voice again, answering before Mr. Andrews could say a word. “It’s your own fault. You were warned.”

The feet of the four men moved away. Then there came the same noises again as the boys had heard before. They were made by the hole in the wall closing up, but the boys didn’t know that. They couldn’t imagine what they were. The noises stopped and there was dead silence. There was also pitch darkness. The three boys strained their ears, and felt sure that the men had gone.

“Well! The brutes! Whatever are they up to?” said Julian in a low voice, trying to loosen the ropes round his hands.

“They’ve got some secret to hide,” said Dick. “Gosh, they’ve tied my feet so tightly that the rope is cutting into my flesh.”

“What’s going to happen?” came Jock’s scared voice. This adventure didn’t seem quite so grand to him now.

“Sh!” said Julian suddenly. “I can hear something!”

They all lay still and listened. What was it they could hear?