"I'm not sure what a mirage is," Tom said, "but it looks like a prison. P'raps we've walked to Dartmoor and didn't know it. My feet feel as if we had."

Mary tucked Mackie under one arm and then felt for Peter's hand. "I hate it," she said and shuddered.

"Looks to me as if there's a pair of big wooden gates in the wall at the bottom of the hill here," said Jon. "Tom's right. It does look like a prison, and it looks empty too."

"Let's go and ask where we are and for a drink of water," was Dickie's bright suggestion

"I can't think of anything I'd hate more than a drink of water," Tom replied. "But we'd better go and see if anyone lives there and can help us."

After some argument Jon, David and Tom went down to explore.

"And don't any of you move from here," were David's parting words. "Look after them, Peter."

As soon as they were clear of the trees they noticed something else very odd about this strange house.

"Look to the right of those big doors," Tom said. "It seems as if there's a big bank stretching along in front of the walls."

"You're right, Tom," David replied. "It might almost be the wall of a moat.''

"I bet it is," Jon said promptly. "I bet that's Offa's Dyke that old Cantor told us about... Look! It runs in a straight line as far as you can see on that side of the house and I dare say that it goes up the hill the other side if we could only see properly... This is an odd sort of place. Those walls must be at least eight feet high and it looks to me as if they've got broken glass on the top... Wonder if they want to stop people from getting in or prevent them from getting out... And I still can't understand why we didn't see it before we got to that little wood."

"Here we are, anyway," David said. "And what do we do now? I shouldn't think anyone has lived here for years."

"I believe they have," Jon said looking at the ground. "This track has been used recently, anyway... Surely there's a bell somewhere?"

They found a rusty iron bell-pull on the brick pillar at the right-hand side of the wooden gates. Tom reached up and pulled it heartily, but although they listened intently for an answering peal no sound broke the silence.

"I'm sure that bell has been used," Tom said. "It pulls easily enough and it didn't squeak. You try it, David."

So David tried, but with no more success, and while they stood there uneasily in the dark wondering what was the best thing to do there came the sound of the peewit's whistle.

"That's Peter or Dickie," David said at once. "They're the best whistlers - I wonder what's wrong?"