“All right. Let me go, you brute. Here’s the key! You go and let my Dad out before the police come! I don’t want him caught!”

Markhoff gave an exclamation of triumph, and snatched a shining key out of Jo’s hand. He gave her a resounding box on the ear.

“You little toad! You can just stay down here with the others, and it’ll be a very, very long stay! Do you know what we’re going to do? We’re going to roll a big rock over the hole in that other cave’s roof — and you’ll be prisoners!”

“You can’t escape upwards — and you won’t be able to escape downwards. You’ll be dashed on the rocks by the sea if you try to swim away. That’ll teach you to interfere!”

The other two men guffawed. “Good idea Mark,” said one. “They’ll all be nicely boxed up here and nobody will know where they are! Come on — we’ve no time to lose. If Red isn’t unlocked soon he’ll go mad!”

They made their way into the heart of the cliff again, and the listening children heard their footsteps getting fainter. Finally they ceased altogether, as one by one the men levered themselves up through the hole in the roof of the last cave, and disappeared up the narrow, low-roofed tunnel that led to the courtyard.

Julian came out from his hiding-place, looking grim and rather scared. “That’s done it!” he said. “If those fellows really do block up that hole — and I bet they have already — it looks as if we’re here for keeps! As he said, we can’t get up, and we can’t escape down — the sea’s too rough for us to attempt any swimming, and the cliff’s unclimbable above the ledge!”

“I’ll go and have a look and see if they have blocked up that hole,” said Dick. “They may be bluffing.”

But it hadn’t been bluff. When Julian and Dick shone their torches on to the hole in the roof, they saw that a great rock was now blocking it up.

They could not get through the hole again. It was impossible to move the rock from below. They went soberly back to the front cave and sat out on the ledge in the light of the sinking sun.

“It’s a pity poor Jo was found,” said George. “And an even greater pity she had to give up the key! Now Red and the others will go free.”

“They won’t,” said Jo, surprisingly. “I didn’t give them the key of the tower room. I’d another key with me — the key of the kitchen larder! And I gave them that.”

“Well, I’m blessed!” said Julian, astounded. “The things you do, Jo! But how on earth did you happen to have the key of the larder?”

Jo told them how she had taken it out and locked herself in when she was having a meal there.