To Mr. Goon’s enormous astonishment he saw the face of “that Frenchy fellow” looking down at him! Yes, there was no doubt about it - there was the black curly hair, the pale face, the sticking-out teeth.

“Gr-r-r-r-r-r!” said Mr. Goon, so angry that he couldn’t speak properly. Fatty, blinded by the glare of the torch, blinked and hastily put the heavy lid back on the entrance to the coal-hole.

Then, afraid that his prisoner might do as he had done and climb out, Fatty dragged a barrel over the hole and stood it on top of the lid. It was about a quarter full of icy water, and it was quite certain that whoever was now down in the cellar could not get out either through the door or through the hole.

Fatty breathed more easily. The prisoner in the cellar began to shout and yell. But hardly a sound came up. Fatty did not think any one would hear the captive.

He crept silently round the hedges of the garden, on the look-out for any one else. But he saw nobody.

Then he heard a curious noise. What could it be? It was like a low and distant humming or throbbing.

“Sounds like an aeroplane,” said Fatty, puzzled. He looked up. To his surprise he saw what looked like a beam of light shining from the roof of Milton House.

“There’s a light of some sort being shown up there,” thought Fatty. “Could that be an aeroplane making that noise - and could that be a light to guide it to the fields near by? They are big enough for an aeroplane to land on them, that’s certain.”

The boy waited for a while. The noise came nearer. It seemed to circle round. Then, after a while, it stopped. Fatty felt certain it was an aeroplane that had landed in the fields behind Milton House. The beam on the roof-top of Milton House went out.

Fatty went into the summer-house, cuddled himself in the rugs there, and waited. Presently, in at a gate that led into the back part of the garden, came the sound of footsteps and the light of a lantern. Evidently the aeroplane passengers were to meet some one at Milton House!

Fatty suddenly felt terribly afraid. He didn’t understand at all what was going on. He only knew it was a mystery, and a dangerous mystery, and he had better get out of it as soon as ever he could.

Had the others read his secret message? Had they telephoned to Inspector Jenks? Were they doing something to help him? No one, as far as he knew, had come in search of him since Pip had taken the note. Fatty thought he had better go back to Pip’s or Larry’s and really find out if anything had been done. If something wasn’t done soon, the men would finish up their business, whatever it was, and clear off for good.

They would never come back to Milton House again, that was certain. They had been using it secretly for some time, but now that their meeting-place, or hiding-place, had been discovered, it would be of no use to them.

“So, unless I can get help straightaway, these men may escape for good!” thought Fatty. “Anyway, at any moment they may find I’ve escaped from that room, and be alarmed. They have only got to hop into that aeroplane and be off to another country if they wish!”

He slipped through the hedge into Chestnut Lane. He crept quietly up the lane, still keeping in the darkness of the hedge.

And quite suddenly he bumped hard into some one who was creeping down the lane, also keeping well in the shelter of the hedge! That some one clutched hard at Fatty, and held him tightly in a grip there was no getting away from.

A light was flashed into his eyes and a grim voice said, “And who are you, and what are you doing here?”

It was a voice Fatty knew well. He listened in delighted surprise.

“Inspector Jenks! Golly, I am glad to hear you!”

The torch flashed into Fatty’s face again.

“You know me?” said Inspector Jenks’ voice. “Who are you?”

The Inspector did not recognize Fatty in his curious disguise. Also Fatty was now extremely black and dirty, and looked more like a negro than himself.

“I’m Frederick Trotteville,” said Fatty. “I’m - er - disguised, Inspector, that’s all.”

“Quiet, now,” said the Inspector, and pulled Fatty into a field beyond the hedge. “Talk in a whisper. What are you doing here? The others telephoned to me and told me enough to puzzle me. I can’t say I thought very much of their story, but I came over to see what was up.”

“Good!” said Fatty. “The others guessed then that I had written a secret message, and they read it.”

“Yes,” said Inspector Jenks. “Well, as I said, I came over as soon as I could by car, and after I had heard what the others had to say, I went to see Mr. Goon. I wanted to see if he knew anything about this, because it was quite likely he did, and hadn’t told you.”

“Oh!” said Fatty. “We didn’t want Clear-Orf to know about it.”

“Well, he doesn’t,” said Inspector Jenks. “He wasn’t there, and no one knows where he is. Do you?”

“No,” said Fatty, not dreaming that Mr. Goon was well and truly locked into the coal-cellar of Milton House.

“Then I thought I’d come along down to Milton House myself,” said the Inspector, “and I bumped into you. What has been happening, Frederick? Is it really something serious, or just a little local robbery or something?”

“I don’t know what it is, sir,” said Fatty. “I really don’t. I can’t make it out. I’ll tell you what I know.”

So the boy related everything: he told of the secret room he had been locked in - the two men he had seen - the one he hadn’t seen, called Jarvis - the coming of the aeroplane, bringing more men to meet in the secret room - and how he had locked somebody into the cellar.

“So you’ll catch one of the men, anyway, sir,” he said, “even if the others escape. Oh! - I nearly forgot - I - er - I managed to get hold of this book for you to see. I thought it might tell you something. I don’t understand a word of it.”

By the light of his torch Inspector Jenks examined the queer little notebook that Fatty had taken from the cupboard in the secret room. He whistled.

“Yes - I understand this all right!” he said, and Fatty heard the real excitement in his low voice. “This is a code-book containing the names, both true and false, of members of a well-known gang and their various addresses! Pretty good work on your part, Frederick. Now, look here, you scoot up to the nearest telephone, ring the number I tell you, and say I want all the Squad down here immediately. There’s not a moment to spare. Immediately! Understand?”

Fatty understood. He felt thrilled. The other mysteries he and the Find-Outers had solved had been exciting, but really, this one was the most exciting of the lot. He shot off up the lane, leaving the Inspector to do a little more watching.

He got the number immediately. It was evidently a private police number. He gave his message. A sharp, commanding voice answered him:

“Right! Over in about ten minutes’ time.”

Fatty rang off. His heart beat fast. What should he do now? Surely he must go down and see what was going to happen? It promised to be extremely exciting.

On the other hand, would it be fair to leave the other Find-Outers out of this? They would so love to be in it too. Surely there wouldn’t be any danger if they all kept in the lane?

Fatty sped off to Pip’s. By good luck all the other Find-Outers were there, very worried, but very glad to think that Inspector Jenks had come and taken charge of things.

Buster suddenly began to bark his head off, and Bets knew that Fatty was coming up the stairs. She ran to the door, flung her arms round him, and dragged him into the room.

“Fatty! Are you safe? How did you get out? Oh, Fatty, we were so worried about you!”

“Get me some biscuits or something,” said Fatty. “I’m starving. You needn’t have worried about me. I was perfectly all right.”