“Fatty must have solved the mystery,” she said. “Isn’t he awfully clever?”

“Let’s put on our things and go and fetch Larry and Daisy now,” said Pip. “Fatty will be expecting us as soon as possible. We’ll march up to the front door and knock loudly.”

They put on their things and ran all the way to Larry’s house. They went in at the garden door and whistled for Larry, using the signal they always kept for themselves.

“Here we are, up here,” said Daisy, popping her head out of a room upstairs. “Any news?”

“Yes, heaps,” said Pip, leaping up the stairs two at a time. “We went to call on Fatty this morning, and the maid said he hadn’t been home all night!”

“Goodness!” said Daisy.

“So I went down to Milton House, without Bets or Buster,” said Pip. “And suddenly this letter floated out of a window! It’s from old Fatty.”

He showed it to Larry and Daisy. They read it in great excitement.

“I say! He’s certainly found out something!” said Larry. “He must have got in at the coal-hole and gone up to that secret room. I vote we all go down to Milton House now, this very minute.”

“Bets was awfully silly all last night and this morning,” said Pip. “She kept on worrying and worrying because she felt sure Fatty was in trouble! She cried like anything when we found he wasn’t at home. She’s an awful baby.”

“I’m not,” said Bets, going red. “I did feel awfully worried, but I couldn’t help it. Something sort of told me that Fatty was in danger - and, as a matter of fact, I still don’t feel quite right about him. I mean - I’ve still got that uncomfortable sort of feeling.”

“Have you?” said Daisy. “How funny! But nothing can be wrong with Fatty now! You’ve read his note.”

“I know,” said Bets, and she read it again. “I wonder why he signed himself ‘Freddie,’ ” she said suddenly. “He nearly always puts ‘Fatty’ now. I suppose he just didn’t think.”

The little girl looked thoughtfully at the letter. Then she sniffed a little, turning this way and that.

“What’s the matter? You look like Buster when he smells a nice smell and doesn’t quite know where it comes from!” said Larry.

“Well - I did get a whiff of a smell that reminded me of something,” said Bets. “What was it now? Yes - I know - oranges! But there aren’t any in the room.”

“Imagination,” said Pip. “You’re always imagining things.” He took the letter and began to fold it up, but as he did so, he too began to sniff.

“How funny! I can smell oranges too now!” he said.

Bets suddenly snatched the letter from him, her eyes bright. She held it to her nose.

“This is what smells of oranges!” she said excitedly. “Smell it, all of you.”

They smelt it. Yes, it smelt of oranges - and that could only mean one thing. Fatty had written another letter on the same sheet - in orange juice, for secret ink!

Bets sat down suddenly because her knees began shaking.

“I’ve got that feeling again,” she said earnestly. “You know - that something is wrong with Fatty. Let’s test the letter quickly for secret writing.”

Daisy flew down to get a warm iron. It seemed ages to wait whilst it got hot enough. Then Pip deftly ran the warm iron over the letter.

At once the secret message came up, faintly brown. The children read it with beating hearts:

“DEAR FIND-OUTERS - Don’t take any notice of the visible letter. I’m a prisoner here. There’s some very dirty work going on; I don’t quite know what. Get hold of Inspector Jenks AT ONCE and tell him everything. He’ll know what to do. Don’t you come near the place, any of you. - Yours ever, ‘FATTY.’ ”

There was a silence. The Find-Outers looked solemnly at one another. Suddenly their mystery seemed to be very deep and dark and dangerous. Fatty was a prisoner! Why had he written that other letter in ink?

“The men who caught him must have made him write it!” said Larry, thinking hard. “They wanted us all to be caught - because we know about the secret room. But clever old Fatty managed to write a secret letter on the same paper.”

“We nearly didn’t find out about the secret one,” said Daisy. “My goodness! - we were just going down to Milton House - to knock at the door - and it would have opened, and we’d have gone in - and we would have been prisoners too.”

“I think we were all very feeble not to think of testing for a secret message,” said Pip. “We ought to have done that as a matter of course.”

“Bets and her sniffing saved us,” said Larry. “If she hadn’t smelt the orange juice, we would all have been in the soup! Good old Bets! She’s really a fine Find-Outer. She found out about the secret message.”

Bets glowed with pleasure at this praise. “My uncomfortable feeling about Fatty was right, wasn’t it?” she said. “Oh dear! - I hope he isn’t too unhappy. Pip, shall we telephone the Inspector at once? I feel as if I want to tell him everything as soon as possible.”

“I’ll telephone now,” said Larry. He went down the stairs with the others, and took up the telephone receiver. He asked for Inspector Jenks’ number. He lived in the next big town.

But alas, the Inspector was out and would not be back for an hour. What was to be done?

“It’s no good going down to Milton House,” said Larry. “Not a bit. If those men have caught Fatty, they would somehow catch us, and then we couldn’t be any help to him at all. We’ll have to wait patiently.”

“It - it would be silly to tell Clear-Orf, wouldn’t it?” said Bets. She disliked Mr. Goon extremely, but she felt that it was very urgent to get help to Fatty.

“What! Make old Clear-Orf a present of our mystery!” said Pip, in disgust. “You’re mad, Bets. Anyway, he’s in bed with a cold. Our charwoman, who goes to turn out for him, told me that this morning. He won’t be snooping down to Milton House for a bit.”

But Pip was wrong. It was true that Mr. Goon had kept in bed for one day, but the next morning he was up and about, still sniffing and sneezing, but quite determined to go down to Milton House as soon as he could.

In fact, even as Pip was telling Bets that Mr. Goon would not be going down to Milton House for a bit, he was on his way there! He had to walk, because the snow was still lying thickly. He set off over the hill, and came to Chestnut Lane.

He noticed the car-wheels going down the lane, and wondered if they went as far as Milton House. He felt pleased when he saw that they stopped outside.

“Ho! Somebody coming to this old empty house in a fine big car!” said Mr. Goon to himself. “A bit funny, that. Yes - there’s something going on here - and those kids have got wind of it. Well, if they think they’re going to have another mystery all to themselves, they’re mistaken!”

Mr. Goon became all business-like. He hitched up his belt. He put his helmet more firmly on his round head. He walked very cautiously indeed to the gate of Milton House, trying to keep out of sight of the windows.

He saw the many footprints leading to and from the front door. He scratched his head, thinking hard. It looked as if people might be there. Were they the rightful owners of the place? What were they doing? And why did the children keep messing about there? Could it be that the thieves of the Sparling Jewels were there, hiding their booty?

Mr. Goon longed to get into that empty house. He longed to explore it. He wanted, however, to explore it without being seen. He felt sure the children had done so.

It was beginning to get dark, for it was a very gloomy, lowering winter’s afternoon, with more snow to come. Mr. Goon went cautiously round the house, and, to his enormous surprise, suddenly saw a black hole in the ground near the kitchen.

Almost at once he saw it was a coal-hole with the iron lid off. He stared at it in surprise. Had somebody got down there? Yes - one of those tiresome children, probably - and maybe they were even now exploring that house to find if any stolen goods were hidden there.