"Bet it's old Cantor," Jon said.

"If it is, then the twins are spying on him," was David's comment. "Look, both of you! The tracks here are clearer than ever, and I'm sure there are marks of car tyres as well."

"It's obvious enough," Jon said as he examined the tracks, "that if we are to fasten anything on to the people who live in that place we've got to have some proof of what they're up to... I mean it's no use going back to Alan Denton or to the police and saying that there are lorry tracks here."

"I'm sure the only way to do that is to get inside the place and see what's happening there," said David.

Tom laughed sarcastically. "You are bright, aren't you? And have you thought how we're going to get past those locked doors or climb those high walls with broken glass on the top?"

"Of course I have. I've just had the brainwave. There's only one way to get in, and that is when the gates are opened."

The others stopped and looked at him as if he was mad.

"I know! You needn't look like that. The way to get in is on the back of, or behind, a lorry when it comes down the track. I'm sure they do come down this way sometimes, and I'd bet that's just about the only time they open the gates. I think our best plan is to hide in the little wood, or, better still, much nearer the gates if we can get down there without being seen, and then when the lorry stops or slows down, try to hop on the back or slip in behind it. Are you game, and can you think of anything better?"

Jon shook his head. "I can't, and although it's crazy I'll have a go. I agree that it's the only way to get a chance of seeing inside. But I think it would be mad for all three to try and get in at the same time. Two's one too many really, but then perhaps we ought to hunt in pairs, so maybe we'd better toss for it."

"I reckon I ought to be one of those who try it," Tom said. "It's my turn to have some fun, and I don't like sheep stealers. Let me go, anyway, David."

But before either of the others could answer Tom gave a whoop of joy and pounced on three empty milk bottles lying in the heather at the edge of the path just as they had been tossed by some lazy, careless picnicker in the past.

"I've got the idea," he shouted triumphantly. "Listen! Let's bust up those bottles and spread the broken glass in the track fairly near the gates, so that when the lorry comes the tyres are punctured and they just have to stop."

"Tom, you're a mastermind!" said Jon.

By now they had reached the shelter of the wood.