"... And then she slipped into the passage and closed the secret panel and that's how she vanished, just like an old witch," Dickie finished triumphantly.

Jon beamed at them.

"Of course you're right! Don't you think so, Penny? That explains everything, doesn't it?"

"Yes, Jon. I think they're right. It would explain how Slinky got in here on Sunday and stole the clue..."

"Yes, and it explains the footmark in the dirt, too! Now, come on all of you and see if we can find the secret of the panel... Stand there a sec. Penny and I'll go and look from the door and see if that's the right place... Yes, that's it. I'm positive."

"If you're right," David said, "there must be something to push or pull on this side, else she couldn't have got back."

"Unless she left the door open," Penny said as she began to run her fingers up and down the smooth panelling.

The twins went down on their knees and began to search the wainscot as Mary said.

"I wish I knew what all this was about. I just happened to think of this secret passage business 'cos it looks that sort of house. But what I want to know is, why?"

"Why what?"

"Why we're doing all this, you silly ass, Dickie. I mean, I can't see why... You'd better tell us everything, Jon. Just tell us why that painter woman should want to come up to your room... Unless she's living here, of course," she added as a bright afterthought.

Jon, David and Penny were working feverishly now to find some catch or part of the smooth woodwork which would prove to be the key to the panel, and as they searched Jon told them about the clue and "earthen vessels" and of how they were sure that Miss Ballinger had not yet deciphered this.

Mary hissed triumphantly. "I've got the place! Watch me... Watch us, I mean."

They saw her poke her finger into a small round hole where two floorboards reached the panelling of the wall. There came a muffled click and slowly, very slowly, the panel adjoining the fireplace swung outwards into the room, disclosing a dark' cavity within. And as it opened there came, too, a breath of dank, cold air - a smell of fungus and wet wood and decay.

Jon then closed the panel softly to within a quarter of an inch of the latch and beckoned them to the centre of the room.

"Now," he began quietly. "Let's decide quickly what's the best thing to do. We know the way in, so if we like we can go back to bed now and explore this passage properly in the morning. Or we can explore it now, but if we do I think we'd better get at least two more torches, and we'd all better put rubber shoes on if we've got them, because it looks and smells damp in there,"