There was nothing more to be done until Monday morning. The children felt impatient, but they couldn’t hurry the coming of Monday, or of the bus either.

Fatty had entered a few notes under his heading of Clues. He had put down all about the anonymous letters, and the post-marks, and had also pinned to the page the tracings he had made of the printed capital letters.

‘I will now write up the case as far as we’ve gone with it,’ he said. ‘That’s what the police do - and all good detectives too, as far as I can see. Sort of clears your mind, you see. Sometimes you get awfully good ideas when you read what you’ve written.’

Every one read what Fatty wrote, and they thought it was excellent. But unfortunately nobody had any good ideas after reading it. Still, the bus passengers to Sheepsale might provide further clues.

The five children couldn’t help feeling rather excited on Monday morning. Larry and Daisy got rather a shock when their mother said she wanted them to go shopping for her - but when she heard that they were going to Sheepsale market she said they could buy the things for her there. So that was all right.

They met at the bus stopping-place ten minutes before the bus went, in case Fatty had any last-minute instructions for them. He had!

‘Look and see where the passengers are sitting when the bus comes up,’ he said. ‘And each of you sit beside one if you can, and begin to talk to him or her. You can find out a lot that way.’

Bets looked alarmed. ‘But I shan’t know what to say!’ she said.

‘Don’t be silly,’ said Pip. ‘You can always open the conversation by saying, “Isn’t that a remarkably clever-looking boy over there?” and point to Fatty. That’s enough to get any one talking.’

They all laughed. ‘It’s all right, Bets,’ said Fatty. ‘You can always say something simple, like “Can you tell me the time, please?” Or, “What is this village we’re passing now?” It’s easy to make people talk if you ask them to tell you something.’

‘Any other instructions, Sherlock Holmes?’ said Pip.

‘Yes - and this is most important,’ said Fatty. ‘We must watch carefully whether anybody posts a letter in Sheepsale - because if only one of the passengers does, that’s a pretty good pointer, isn’t it? The post-office is by the bus-stop there, so we can easily spot if any one catches the 11.45 post. We can hang around and see if any of the bus passengers posts a letter before that time, supposing they don’t go to the letter-box immediately. That’s a most important point.’

‘Here comes the bus,’ said Bets in excitement. ‘And look - there are quite a lot of people in it!’

‘Five!’ said Larry. ‘One for each of us. Oh gosh! One of them is old Clear-Orf!’

‘Blow!’ said Fatty. ‘So it is. Now whatever is he doing on the bus this morning? Has he got the same idea as we have, I wonder? If so, he’s brainier than I thought. Daisy, you sit by him. He’ll have a blue fit if I do and I know Buster will try to nibble his ankles all the time.’

Daisy was not at all anxious to sit by Mr. Goon, but there was no time to argue. The bus stopped. The five children and Buster got in. Buster gave a yelp of joy when he smelt the policeman. Mr. Goon looked round in astonishment and annoyance.

‘Gah!’ he said, in tones of deep disgust. ‘You again! Now, what you doing on this bus today? Everywhere I go there’s you children traipsing along!’

‘We’re going to Sheepsale market, Mr. Goon,’ said Daisy politely, sitting beside him. ‘I hope you don’t mind. Are you going there too?’

‘That’s my business,’ said Mr. Goon, keeping a watchful eye on Buster, who was trying to reach his ankles, straining at his lead. ‘What the Law does is no concern of yours.’

Daisy wondered for a wild moment if Mr. Goon could possibly be the anonymous letter-writer. After all, he knew the histories of everyone in the village. It was his business to. Then she knew it was a mad idea. But what a nuisance if Mr. Goon was on the same track as they were - sizing up the people in the bus, and going to watch for the one who posted the letter to catch the 11.45 post.

Daisy glanced round at the other people in the bus. A Find-Outer was by each. Daisy knew two of the people there. One was Miss Trimble who was companion to Lady Candling, Pip’s next-door neighbour. Larry was sitting by her. Daisy felt certain Miss Trimble - or Tremble as the children called her, could have nothing to do with the case. She was far too timid and nervous.

Then there was fat little Mrs. Jolly from the sweet-shop, kindness itself. No, it couldn’t possibly be her! Why, every one loved her, and she was exactly like her name. She was kind and generous to everyone, and she nodded and smiled at Daisy as she caught her eye. Daisy was certain that before the trip was ended she would be handing sweets out to all the children!

Well, that was three out of the five passengers! That only left two possible ones. One was a thin, dark, sour-faced man, huddled up over a newspaper, with a pasty complexion, and a curious habit of twitching his nose like a rabbit every now and again.

This fascinated Bets, who kept watching him. The other possible person was a young girl about eighteen, carrying sketching things. She had a sweet, open face, and very pretty curly hair. Daisy felt absolutely certain that she knew nothing whatever about the letters.

‘It must be that sour-faced man with the twitching nose,’ said Daisy to herself. She had nothing much to do because it was no use tackling Mr. Goon and talking to him. It was plain that he could not be the writer of the letters. So she watched the others getting to work, and listened with much interest, though the rattling of the bus made her miss a little of the conversation.

‘Good morning, Miss Trimble,’ Daisy heard Larry say politely. ‘I haven’t seen you for some time. Are you going to the market too? We thought we’d like to go today.’

‘Oh, it’s a pretty sight,’ said Miss Trimble, setting her glasses firmly on her nose. They were always falling off, for they were pince-nez, with no side-pieces to hold them behind her ears. Bets loved to count how many times they fell off. What with watching the man with the twitching nose and Miss Trimble’s glasses, Bets quite forgot to talk to Mrs. Jolly, who was taking up most of the seat she and Bets was sitting on.

‘Have you often been to Sheepsale market?’ asked Larry.

‘No, not very often,’ said Miss Trimble. ‘How is your dear mother, Laurence?’

‘She’s quite well,’ said Larry. ‘Er - how is your mother, Miss Tremble? I remember seeing her once next door.’

‘Ah, my dear mother isn’t too well,’ said Miss Trimble. ‘And if you don’t mind, Laurence dear, my name is Trimble, not Tremble. I think I have told you that before.’

‘Sorry. I keep forgetting,’ said Larry. ‘Er - does your mother live at Sheepsale, Miss Trem - er Trimble? Do you often go and see her?’

‘She lives just outside Sheepsale,’ said Miss Trimble, pleased at Larry’s interest in her mother. ‘Dear Lady Candling lets me go every Monday to see her, you know - such a help. I do all the old lady’s shopping for the week then.’

‘Do you always catch this bus?’ asked Larry, wondering if by any conceivable chance Miss Trimble could be the wicked letter-writer.

‘If I can,’ said Miss Trimble. ‘The next one is not till after lunch you know.’

Larry turned and winked at Fatty. He didn’t think that Miss Trimble was the guilty person, but at any rate she must be put down as a suspect. But her next words made him change his mind completely.

‘It was such a nuisance,’ said Miss Trimble. ‘I lost the bus last week, and wasted half my day!’

Well! That put Miss Trimble right out of the question, because certainly the letter-writer had posted the letter to poor Gladys the Monday before - and if Miss Trimble had missed the bus, she couldn’t have been in Sheepsale at the right time for posting!

Larry decided that he couldn’t get any more out of Miss Trimble that would be any use and looked out of the window. Bets seemed to be getting on well with Mrs. Jolly now. He couldn’t hear what she was saying, but he could see that she was busy chattering.

Bets was getting on like a house on fire! Mrs. Jolly greeted her warmly and asked after her mother and father, and how the garden was, and had they still got that kitchen cat that was such a good hunter. And Bets answered all her questions, keeping an interested eye on Miss Trimble’s glasses, which had already fallen off twice, and on the sour-faced man’s twitching nose.

It was not until she saw how earnestly Fatty was trying to make the sour-faced man talk to him that she suddenly realized that she too ought to find out a few things from Mrs. Jolly. Whether, for instance, she always caught this bus!

‘Are you going to the market, Mrs. Jolly?’ she asked.

‘Yes, that I am!’ said Mrs. Jolly. ‘I always buy my butter and eggs from my sister there. You should go to her stall too, Miss Bets, and tell her you know me. She’ll give you over-weight in butter then and maybe a brown egg for yourself!’

‘She sounds awfully kind - just like you’ said Bets.

Mrs. Jolly was pleased and laughed her hearty laugh. ‘Oh, you’ve got a soft tongue, haven’t you?’ she said. Bets was surprised. She thought all tongues must surely be soft.

She looked at Mrs. Jolly, and decided not to ask her any more questions about going to Sheepsale every Monday because nobody, nobody with such kind eyes, such a lovely smile, such a nice apple-cheeked face could possibly write an unkind letter! Bets felt absolutely certain of it. Mrs. Jolly began to fumble in her bag.

‘Now where did I put those humbugs?’ she said. ‘Ah, here they are? Do you like humbugs, Miss Bets? Well, you help yourself, and we’ll pass them over to the others as well.’

Pip was sitting by the young girl. He found it easy to talk to her.

‘What are you going to paint?’ he asked.

‘I’m painting Sheepsale market,’ she answered. ‘I go every Monday. It’s such a jolly market - small and friendly and very picturesque, set on the top of the hill, with that lovely country all round. I love it.’

‘Do you always catch the same bus?’ asked Pip.

‘I have to,’ she said. ‘The market’s in the morning, you know. I know it by heart now - where the hens and ducks are, and the sheep, and the butter-stalls and the eggs and everything!’

‘I bet you don’t know where the post-office is!’ said Pip quickly.

The girl laughed and thought. ‘Well, no, I don’t!’ she said. ‘I’ve never had to go there and so I’ve never noticed. But if you want it, any one would tell you. There can’t be much of a post-office at Sheepsale, though. It’s only a small place. Just a market really.’

Pip felt pleased. If this girl didn’t know where the post-office was, she could never have posted a letter there. Good. That ruled her out. Pip felt very clever. Anyway, he was certain that such a nice girl wouldn’t write horrid letters.

He looked round at the others, feeling that his task was done. He felt sorry for Daisy, sitting next to the surly Mr. Goon. He wondered how Fatty was getting on.

He wasn’t getting on at all well! Poor Fatty - he had chosen a very difficult passenger to talk to.