So this time Penny led the way down until they reached Mr. Grandon's room. She listened carefully at the panel and whispered, "There's no sound. I think the nasty little man must be asleep... Here goes," and she rapped sharply on the panel three times. She repeated this signal twice and then whispered, "I heard a click. He's put the light on. Now listen to me," and in a very creditable imitation of Miss Ballinger she went on, "Open quickly! Urgent! I have lost my light and cannot find the catch. Are you there? Open quickly. Do not keep me waiting."

There was a startled gasp from the other side of the panelling.

"Why have you come back? Go away. It's not safe."

Penny took a deep breath and tried again.

"Do as I say," she rumbled. "Open up and do not argue."

"Very well, but be quick, I beg you," Grandon gasped, and Penny found herself pushed into the background with the twins while Jon and David took her place in front of the panel which suddenly swung open. For a moment they were all dazzled by the light, and then the two boys jumped down into the room. Grandon, now in scarlet pyjamas and a brilliant patterned dressing-gown, started back in astonishment. His mouth fell open, and when Penny turned to help the twins he stuttered with rage.

"Please don't make a noise, Mr. Grandon. We got lost in there and we want to get off to bed right away. Let us out through your room, please, and we're sorry we got you out of bed."

The man gulped and put his hand to his throat. Penny, watching him curiously, saw the veins swell on his forehead.

"What do you mean?" he gasped in a strangled voice. "How did you get here? What's in there? A passage? I suppose this is all a trick just to wake me up and annoy me. Tell me quickly. Is that a passage?"

Nobody answered him, and Penny even felt sorry for him. Jon led the way across the room and David followed as Mr. Grandon spoke again.

"I do not know the meaning of this astonishing escapade, but I shall most certainly inform Mrs. Warrender in the morning - and Mr. and Mrs. Morton also," he added after a quick look at David and the twins.

"I wouldn't tell anybody," Jon said steadily. "I honestly don't think you should. I hope you will believe what I say, Mr. Grandon. Much better for you to say absolutely nothing to absolutely nobody."

Slinky was standing now between them and the door. His lips were shaking, but Penny did not like the look in his eyes, for they were blazing with hatred as Dickie said:

"If you didn't know there was a passage there, why did you open the panel for us?"

"I shall most certainly inform your parents in the morning," he said quietly. "Now get out! All of you!"