At last he gave it up. His prey had escaped him - but next time - ah, next time he saw any one with those awful teeth, he’d get them! There was something funny about two people having the same sticking-out teeth.

“I never did see teeth that stuck out so,” thought the defeated Mr. Goon, as he made his way round the side of the house and walked to the front gate. “That Frenchy fellow had them, and so had this one I’m after now. Wish I could have caught him. I’d have asked him a few straight questions, I would!”

Pip was very thankful to see him go. He waited till the policeman had disappeared round the house, and then he cautiously slid along a branch to the window, in order to get a better look inside.

There was no doubt about it at all. The room had plenty of furniture in it - a couch that was big enough for a bed, an arm-chair, two smaller chairs, a table, a book case with books in, a carpet on the floor. It was all most extraordinary.

“There’s an electric fire there too,” said Pip to himself. “But there’s no one there - and judging by the dust everywhere, there hasn’t been any one for some time. I wonder who the house belongs to.”

He looked at the bars on the window. No one could possibly get in or out of the window, that was certain. The bars were as close together as most nursery-window bars are - not even a child could slip between them.

Pip climbed cautiously down the tree, keeping a sharp look-out in case Mr. Goon was lurking somewhere. But that puzzled man had gone back to the village, comforting himself with the thought that though he had lost the boy with the teeth and eyebrows, he had at least got his mackintosh! Wait till he saw if there was a name inside!

Pip felt cold without his mackintosh. He thought ruefully of how he could explain its loss to his mother. Perhaps she wouldn’t notice it was gone. On the other hand, mothers invariably noticed anything like that almost immediately.

The fog was now getting very thick. Pip would have liked to stay and snoop round a bit, but he was afraid of getting lost if the fog grew much thicker. So he contented himself with making quite sure that the house was indeed the empty one he knew.

It was. There was no doubt about it - and the rooms on the ground floor were perfectly empty. On the gate was the name Pip had seen before - Milton House.

“It’s a mystery!” said Pip, as he plodded back in the fog. “A real mystery.” Then he stopped suddenly and hugged himself. “This might be our third mystery! We shall have to solve it somehow. There’s something very queer going on in that old empty house!”

Pip made his way back to Fatty’s house, where the others were waiting for him to report on anything that had happened. Fatty had what he called a “den” - a small crowded room, full of books, games, sports things, and a cosy basket for Buster. The fog clung round Pip and made him feel damp and cold.

He was shivering when at last he went in at the side-door of Fatty’s house. He listened to see it any one was about, because he was not anxious to bump into the maid or Mrs. Trotteville in his present disguise.

He heard nothing, and made his way up the stairs. The others were playing a card-game on the floor. They looked up when Pip came in.

“Oh - here’s Pip!” said Bets, pleased, and Buster went to greet him as if he had not seen him for weeks. “Did you do anything exciting, Pip?”

“I should jolly well think I did!” said Pip, his eyes shining. He got as close to the fire as he could. “And what’s more, Find-Outers - I believe I’ve got our third mystery for you!”

They all stared at him in delight and surprise. Bets jumped up. “Tell us, quick! What do you mean? What is the mystery?”

“I’ll tell you it all from the beginning,” said Pip. “Golly, I’m cold!”

“Where’s your coat?” said Daisy, seeing how cold Pip was.

“Old Clear-Orf has got it!” said Pip. “Sickening, isn’t it?”

“Clear-Orf! But how did he get it?” said Fatty. “Was your name in it?”

“Do you remember if it was, Bets?” asked Pip, turning to his little sister.

“No, it wasn’t,” said Bets. “So Clear-Orf won’t know whose it was - unless he goes round asking our parents if one of us has lost a mack!”

“Don’t worry,” said Fatty. “My old mack is almost exactly like Pip’s. I’ve got a new one. Pip can take mine, then if Clear-Orf goes round asking our parents if we’ve lost one, Pip can produce mine.”

“Thanks, Fatty,” said Pip relieved. “You always come to the rescue. Well - let me tell my story.”

He began, and the children giggled to hear how poor old Miss Frost got such a fright to see the fierce eyebrows, red face, and awful teeth just round the corner - and roared when Pip described what a dance he had led Mr. Goon in the fog.

“Fancy him not looking up into the trees,” said Fatty. “He’ll never make a detective! But you haven’t come to the mystery yet, Pip - what is it?”

“Well,” said Pip importantly, “as you all know, Milton House is empty - has been empty for ages, hasn’t it?”

The others nodded. They all knew the house quite well.

“All right,” said Pip, “well listen to this. One of the rooms at the very top of the house is fully furnished!”

Every one stared in amazement.

“Fully furnished!” said Fatty. “How very extraordinary! Does some one live there after all, then - and if so, why does he live at the top of the house? Pip, this is certainly very queer.”

“It is, isn’t it,” said Pip, pleased at the interest he had caused. “Don’t you think it’s going to be our third mystery? Fm sure there’s something queer about it.”

“Well, it certainly sounds jolly strange,” said Fatty. “Yes, it’s a mystery all right.”

“Hurrah!” said Bets. “We’ve got one for these hols, after all! How shall we solve it?”

“Well - it’s not our usual sort of mystery,” said Fatty thoughtfully. “I mean - in the ones before we have had Clues and Suspects to work on - this time all we’ve got is a fully furnished room at the top of an empty house. We don’t even know if there’s anything wrong about it. But it’s certainly queer and unusual enough for us to try and find out what’s behind it.”

“Ooooh, how lovely!” said Bets joyfully. “I did so want a mystery these hols. Especially as we’ve got so many good detective tricks.”

“Well, Pip, you certainly had a good afternoon,” said Larry. “Do take off that awful disguise now. I can’t bear to look at you. It’s the teeth that make you look so revolting.”

“I know,” said Pip, taking them out and going to a basin to rinse them and dry them. “They’re marvellous. Old Clear-Orf nearly had a fit when he saw them flashing at him again, after seeing them in the French boy’s mouth!”

The others laughed at the thought of Mr. Goon’s surprise. Fatty suddenly looked thoughtful.

“I only hope old Clear-Orf won’t go snooping round after us,” he said. “I know it was fun to make him think we were in the middle of a new mystery he knew nothing about - but now that we really have stumbled on to one, it will be sickening if he follows us around. It will cramp our style terribly.”

“Blow!” said Larry. “We shan’t be able to keep this mystery to ourselves if Clear-Orf sniffs it out. I must say it sounds a first-class one - I find myself asking all kinds of questions! Who uses the room? Why in an empty house? Does the owner know about it? When does the one who uses it come and go?”

“Yes - there are all sort of questions to answer,” said Fatty. “It’s going to be interesting - but difficult! I vote we try and get into the room.”

“On no!” said every one at once.

“We daren’t do that,” said Larry. “We can’t break into houses - even empty ones. You know we can’t.”

“We don’t need to break in,” said Fatty, in a dignified manner. “There’s no reason why we shouldn’t go to the house-agent’s and ask for the key to look over the house, is there?”