Fatty replaced the receiver and rushed upstairs in the greatest excitement. He burst into the play-room and stood dramatically in the doorway.

‘What do you think!’ he said. ‘There’s been another of those beastly letters - sent to Mrs. Cockles’s sister! She got it this morning and is all upset and that’s why Mrs. Cockles didn’t turn up to help Mrs. Moon! And Mrs. Cockles said if I go round to her sister’s, she’ll show me the letter. I simply must find out where it was posted and when.’

‘Golly!’ said everyone.

‘Let me come too,’ said Pip.

‘No. Best for only one of us to go,’ said Fatty. ‘Give Mrs. Moon this message when she comes back, Pip - say that Mrs. Cockles rang up and said she had to go to her sister, who was upset because she’d had a nasty letter. Don’t let on that you know any more than that.’

‘Right,’ said Pip. ‘Well, you hop off now, Fatty, before old Goon gets going on the job. He’ll be round at Mrs. Cockles’s sister in no time, as soon as he hears about the letter.’

Fatty shot off. He knew where Willow Lane was. He found number 9 and went to the little front door. It was a dirty, untidy little place. He rapped on the wooden door.

‘Come in!’ called Mrs. Cockles’s voice. ‘Oh, it’s you, Master Frederick. Well, my sister says she won’t show you the letter. She says what’s in it isn’t for anyone to read but me and the police. And I won’t say but what she’s right, now I’ve read the letter properly.’

Fatty was most bitterly disappointed. ‘Oh, I say!’ he said. ‘You might just let me have a squint. I’ve seen all the others. Go on, be a sport and let me see it.’

Mrs. Cockles’s sister was a fat, untidy woman, who breathed very loudly through her mouth and talked through her nose.

‘’Taint fit for a child to read,’ she said. ‘It’s a right down spiteful letter, and not a word of truth in it, neither!’

‘I’m not a child!’ said Fatty, making himself as tall as he could. ‘You can trust me to read the letter and not say a word to anyone. I’m - er - I’m investigating the case, you see.’

Mrs. Cockles was very much impressed. But she still agreed with her sister that the letter was not one for him to read. Fatty, of course, was not in the least curious about its contents - but he did badly want to see the printing and, of course, the envelope.

‘Well - could I just see the envelope!’ he asked. ‘That would do quite well.’

Neither Mrs. Cockles nor Mrs. Lamb, her sister, could see any reason why he should not see the envelope. They handed it to him. Fatty looked at it eagerly, to make out the post-mark.

But there was none! There was no stamp, no post-mark! Fatty stared in surprise.

‘But - it didn’t come by post!’ he said.

‘I never said it did,’ said Mrs. Lamb. ‘It come this morning, very early - about half-past six, I reckon. I heard something being pushed under the door, but I was too sleepy to get up. So I didn’t get it till about half-past eight - and then I was that upset, I sent for Mrs. Cockles here. And you come at once, didn’t you, Kate?’

‘Course I did,’ said Mrs. Cockles. ‘Only stopped to have a word with Mr. Goon about it. He’ll be along soon to have a look at the letter too.’

Fatty felt slightly alarmed. He didn’t want to bump into Clear-Orf at the moment. He stared hard at the envelope once more. The name and address were printed in capital letters again, and the square envelope was the same as the others that had been used. Fatty took his note-book out of his pocket and looked at the page headed CLUES.

He compared the tracing of the word PETERSWOOD with the same word on the envelope. Yes, there was no doubt at all, but that the same hand wrote both words. They were exactly alike.

Fatty handed the envelope back to Mrs. Lamb. He had got from it all he wanted. He didn’t want to see the letter inside. He could imagine it - a few sentences of spite and hurtfulness, with perhaps a little truth in them. He had enough to puzzle himself with - here was the usual letter, received on a Tuesday morning - but this time not through the post, and not from Sheepsale. Funny!

‘Well, I’ll be going,’ said Fatty. ‘Thanks for showing me the envelope, Mrs. Lamb. I’m so sorry you had one of these beastly letters. I shan’t rest till I find out who is the writer of them.’

‘Mr. Goon, he’s on to them too,’ said Mrs. Cockles. ‘Says he’s got a very good idea who it is, too.’

Fatty doubted that. He was sure that Mr. Goon was as puzzled as he was. He said good-bye and went out of the dirty little room.

But coming in at the front gate was the burly figure of Mr. Goon! Fatty was annoyed. He tried to get out of the gate before Mr. Goon came in, but the policeman, surprised and exasperated at seeing Fatty there, caught hold of his arm. He pulled the boy inside the cottage.

‘Has this boy been interfering with the Workings of the Law?’ he demanded, in an angry voice. ‘What’s he doing here, that’s what I want to know?’

Mrs. Lamb was afraid of Mr. Goon, but Mrs. Cockles was not.

‘He’s not been interfering,’ she said. ‘Only taking a friendly interest like.’

‘How did he know that Mrs. Lamb had received one of these here letters?’ inquired Mr. Goon, still in a furious voice.

‘Well, I had to ring up Mrs. Moon to tell her as how I wouldn’t be along this morning, because my sister had had a letter,’ said Mrs. Cockles. ‘And Master Frederick, he happened to be there, and he took the message. And he said he knew all about the letters and would like to see this one, and I knew he wasn’t half-bad at snooping out things, so...’

‘Mrs. Lamb, you didn’t show this interfering boy that letter before you showed it to me, did you?’ thundered Mr. Goon.

‘Well - well, sir - he did say as he’s seen them all,’ stammered poor Mrs. Lamb, frightened out of her life. ‘So I thought there wouldn’t be much harm. I only showed him the envelope though, Mr. Goon, sir.’

Mr. Goon turned his frog-like gaze on to Fatty. ‘What’s that mean - that you’ve seen all the letters?’ he demanded. ‘They’ve been in my possession - never out of it for a minute. What you mean - you’ve seen them all?’

‘I must have been dreaming,’ answered Fatty, in an amiable voice. This was the voice that drove poor Mr. Goon to fury. He snorted.

‘You’re telling untruths,’ he said. ‘Yes, you know you are. Them letters haven’t been out of my possession, not for one minute!’

‘Haven’t they really?’ said Fatty. ‘Well, I couldn’t have seen them then.’

‘Unless you know more about them than you make out!’ said Mr. Goon, darkly and mysteriously, suddenly remembering how he had seen Fatty post a letter at Sheepsale the morning before. ‘Ho, you’re a deep one, you are - never know what your game is, I don’t! I wouldn’t put anything past you, Master Frederick Trotteville!’

‘Thank you, Mr. Theophilus Goon,’ said Fatty, and grinned. Mr. Goon longed to box his ears. Then he suddenly remembered that those letters had been out of his possession once - that time when he had apparently dropped them in the road, after colliding with the red-haired telegraph-boy. He stared suspiciously at Fatty.

‘That telegraph-boy your friend?’ he asked suddenly. Fatty looked mildly surprised.

‘What telegraph-boy?’ he asked.

‘That red-haired fellow with the freckles,’ said Mr. Goon.

‘I’m afraid I’ve no red-haired, freckled telegraph-boy for a friend, much as I would like one,’ said Fatty. ‘But why all these questions about a telegraph-boy?’

Mr. Goon wasn’t going to tell him. But he made a mental note to get hold of that telegraph-boy and ask him a few questions. Perhaps he and Fatty were in league together!

‘Well, I’ll go now,’ said Fatty politely, ‘unless you’ve got any more questions to ask me about telegraph-boys, Mr. Goon? Oh - and would you like another clue? Wait a bit, I’ll see if I’ve got one about me!’

To Mr. Goon’s rage he felt in his pockets and produced a doll’s straw hat. ‘Now was that a clue?’ murmured Fatty, but, seeing Mr. Goon gradually turning a familiar purple, he moved swiftly through the door.