Meanwhile, not knowing that Mr. Goon was thinking all these tiresome things, the children were on their way to Milton House, keeping a sharp look-out in case Mr. Goon was still following them.

“I don’t think he is,” said Fatty. “He’s probably on his way to Felling Hill by now!”

They came to Milton House - and almost at once Fatty gave a low exclamation.

“Look there!’ What do you think of that? Footprints to the front door!”

The children stared at them. They saw a line of prints, very big prints too, leading down the drive, right to the front door. And they saw another line, criss-crossing the others, leading back!

“Some one’s been here,” said Fatty, excited.

“Yes - I bet you did put John Henry Smith on his guard, and he came down here in the night!” said Larry.

“How did he come?” said Pip.

“By car, I bet!” said Daisy. “I saw some car-prints outside, but I didn’t take much notice of them. Come and see.”

They all went to see - and sure enough, a car had been down Chestnut Lane the night before, and had stopped outside Milton House! And it had turned round there too and gone back up the lane again, for there were the same wheel-prints on opposite sides of the road.

“Now we’re getting somewhere!” said Pip. “We know that whoever you phoned to knew about Milton House, and was worried to know some one had mentioned it, and came down to inspect. Who was it? John Henry Smith? And who is Mr. Smith, anyhow? I wish I knew.”

“Let’s shin up the tree and see if anything is different in the room,” said Larry.

So they all climbed the tree and one by one looked in at the window. And they saw several things that interested them!

“Some one’s put a kettle on top of the electric stove,” said Daisy.

“And some one’s put tins of food on that shelf opposite,” said Pip.

“And there are some books on the window-sill that weren’t there before - books in a foreign language I don’t know,” said Larry.

“And the room’s been dusted,” said Bets. “It looks quite clean. And there are two thick rugs on the sofa. What does it all mean?”

“It means that the room has been got ready for a visitor!” said Fatty. “Yes - it can only mean that. Who’s the visitor? Not Mr. John Henry Smith, I bet! Some one who uses the room at intervals when he wants to be well hidden. It’s jolly queer.”

“I wish we could get in and explore the whole house,” said Pip. “But there’s no way in at all.”

“Wait a minute,” said Fatty, thinking hard. “There may be a way. I’ve just thought. That is, if there’s an outside coal-hole.”

“What do you mean?” said the others, puzzled.

“Come and see,” said Fatty.

So down the tree they went, and, led by Fatty, went round to the kitchen entrance. It began to snow again as they walked round, and Fatty was pleased.

“The snow will hide our footmarks,” he said. “I was a bit worried about those. Ah, look - this is what I hoped to see!”

He pointed down to the ground to a spot that he had rubbed clear of snow with his boot. The others saw a round iron lid, whose crevices were black with old coal-dust.

“An outside coal-hole,” said Fatty. “Now you all know that a coal-hole leads into a coal-cellar - and that steps lead up to the kitchen from the coal-cellar - and so any one slipping down this coal-hole can get into the house!”

“Jolly good, Fatty!” said every one admiringly.

“But do you think we’d better go down in these clothes?” added Pip. “We’d get filthy, and I know my mother would ask all sorts of awkward questions.”

“Yes - we can’t go down now,” said Fatty. “I shall go down myself tonight!”

The others looked at him in awe. To go down to Milton House, the mystery place, at night, and get down the coalhole! It seemed a most heroic feat to every one.

“I shall put on a disguise,” said Fatty. “Just in case.”

“In case of what?” said Bets.

“Oh, just in case,” said Fatty. “I don’t want to be recognized, do I?”

“Oh! - you mean Mr. Goon might see you,” said Bets.

Fatty didn’t mean that at all. He just wanted to disguise himself because he liked it. What was the good of buying disguises if you didn’t use them?

He felt pleased and important. The mystery, as he had said the day before, was decidedly warming up! Soon, no doubt, the Find-Outers would have solved it, and could tell Inspector Jenks all about it.

“We won’t tell the Inspector a word about all this till we’ve got to the bottom of the mystery and can tell him everything, down to the last detail,” said Fatty. “Then, if we find there’s any arresting or anything to be done, he can do it.”

“Oooo - do you think there will be people to be arrested and sent to prison?” said Bets, with large eyes.

“You never know,” said Fatty grandly. “Well - we’d better go now, and I’ll lay my plans for tonight.”

It was most enjoyable talking over Fatty’s plans for the night. All the Find-Outers and Buster gathered round the fire in Pip’s playroom, and talked.

“My mother and father will be away for two days,” said Fatty. “That’s lucky. They won’t know if I’m there tonight or not. I shall go down to the summer-house in the grounds of Milton House and make myself comfortable there with a couple of rugs. If I don’t hear anything by midnight, I shall get in at the coal-hole.”

“Fatty - suppose you’re caught?” said Pip.

“Yes - I’d thought of it,” said Fatty, considering. “If I’m caught, one of you had better know. I’ll tell you what - if I’m caught, I shall throw a note out of the window of whatever room I am locked up in - I imagine if I’m caught I shall be locked in somewhere - and one of you must scout round the grounds tomorrow morning and look out for the note. See? It will be in invisible writing, of course.”

This sounded terribly exciting. Bets looked solemn. “Don’t be caught, Fatty. I don’t want you to be caught.”

“Don’t worry. I’m pretty smart,” said Fatty. “People would have to be pretty clever to catch me!”

“Well - that’s settled, then,” said Larry. “You are going down to Milton House tonight in disguise, and you’re going to wait till midnight to see if any one comes. If nobody comes, you’re going to get down the coal-hole and explore the secret room, to see if you can get any information about the mysterious John Henry Smith. By the way - I do wonder why that window was barred if there were no children in that house.”

“Don’t know,” said Fatty. “But I expect I shall find out.”

“If you don’t get caught, you’ll come back home, go to bed, and meet us in the morning with whatever news you’ve got,” said Larry. “But if you don’t turn up, one of us will snoop round the grounds and wait for a letter written in invisible ink. Don’t forget to take an orange with you, Fatty, in case you have to write that note.”

“Of course I shan’t forget,” said Fatty. “But as I shan’t be caught, you needn’t worry - there won’t be any letter floating out of a window!”

“Anyway, Fatty, you know how to get out of a locked room if you have to,” said Bets.

“Of course!” said Fatty. “I shall be all right, you may be sure.”

As Fatty’s parents were away, the Find-Outers decided to go down to his house after tea and watch him disguise himself. They all felt excited, though Bets had now got the idea that this mystery was a dangerous one, and she was rather worried.

“Don’t be silly,” said Fatty. “What danger can there be in it? I shall be all right, I tell you. This is an adventure, and people like me never say no to an adventure.”

“You are brave, Fatty,” said Bets.

“This is nothing!” said Fatty. “I could tell you of a time when I really was brave. But I expect I should bore you?” He looked round inquiringly.

“Yes, you would bore us,” said Pip. “Are you going to wear those terrible teeth again, Fatty?”