The sour-faced man appeared to be very deep indeed in his paper, which seemed to Fatty to be all about horses and dogs.

Buster sniffed at the man’s ankles and didn’t seem to like the smell of them at all. He gave a disgusted snort and strained away towards where Mr. Goon sat, a few seats in front.

‘Er - I hope my dog doesn’t worry you, sir,’ said Fatty.

The man took no notice. ‘Must be deaf,’ thought Fatty and raised his voice considerably. ‘I hope my DOG doesn’t WORRY you, sir,’ he said. The man looked up and scowled.

‘Don’t shout at me. I’m not deaf,’ he said. Fatty didn’t like to ask again if Buster worried him. He cast about for something interesting to say.

‘Er - horses and dogs are very interesting, aren’t they?’ he said. The man took no notice. Fatty debated whether to raise his voice or not. He decided not.

‘I said, horses and dogs are very interesting, aren’t they?’ he repeated.

‘Depends,’ said the man, and went on reading. That wasn’t much help in a conversation, Fatty thought gloomily. The others were jolly lucky to have got such easy people to tackle. But still - of all the passengers in the bus, this man looked by far the most likely to be the letter-writer - sour-faced, scowling, cruel-mouthed! Fatty racked his brains and tried again.

‘Er - could you tell me the time?’ he said, rather feebly. There was no reply. This was getting boring! Fatty couldn’t help feeling annoyed too. There was no need to be so rude, he thought!

‘Could you tell me the time?’ he repeated.

‘I could, but I’m not going to, seeing that you’ve got a wrist-watch yourself,’ said the man. Fatty could have kicked himself.

‘You’re not being much of a detective this morning!’ he told himself. ‘Buck up, Frederick Algernon Trotteville, and look sharp about it!’

‘Oh - look at that aeroplane!’ said Fatty, seeing a plane swoop down rather low. ‘Do you know what it is, sir?’

‘Flying Fortress,’ said the man, without even looking up. As the aeroplane had only two engines and not four, this was quite wrong and Fatty knew it. He looked at his fellow passenger in despair. How could he ever get anything out of him?

‘I’m going to Sheepsale market,’ he said. ‘Are you, sir?’

There was no answer. Fatty wished Buster would bite the man’s ankles. ‘Do you know if this is Buckle Village we’re passing?’ asked Fatty, as they passed through a pretty little village. The man put down his paper and glared at Fatty angrily.

‘I’m a stranger here,’ he said. ‘I know nothing about Buckle or Sheepsale or its market! I’m just going there to be picked up by my brother, to go on somewhere else - and all I can say is that the further I get away from chatterboxes like you, the better I shall like it!’

As this was all said very loudly, most of the people in the bus heard it. Mr. Goon chuckled heartily.

‘Ah, I’ve had some of him too!’ he called. ‘Proper pest, I reckon he is.’

‘Go and sit somewhere else and take your smelly dog with you,’ said the sour-faced man, pleased to find that somebody else agreed with his opinion of poor Fatty.

So Fatty, red in the face, and certain that he would not be able to get anything more out of the annoyed man, got up and went right to the front of the bus, where nobody was sitting. Bets was sorry for him and she left Mrs. Jolly and joined him. Larry, Pip and Daisy came across too, and they talked together in low voices.

‘I can’t see that it can be any one here,’ said Fatty, when he had heard all that the others had to say. ‘It’s obviously not old Clear-Orf - and we can rule out Miss Tremble and Mrs. Jolly surely. And I agree with Pip that the artist girl isn’t very likely either, especially as she doesn’t even know where the post-office is. And my man said he was a stranger here, so it doesn’t look as if he could be the one. A stranger wouldn’t know any of the Peterswood people.’

‘Does he come on this bus every Monday?’ asked Pip, in a low voice.

‘I didn’t get as far as asking him that,’ said Fatty gloomily. ‘Either he wouldn’t answer, or he just snapped. He was hopeless. It doesn’t look really as if any of the people here could have posted those letters.’

‘Look - there’s somebody waiting at the next bus-stop!’ said Bets suddenly. ‘At least - it isn’t a bus-stop - it’s just somebody waving to the bus to stop it for himself. That must be the person we want, if there’s nobody else.’

‘Perhaps it is,’ said Fatty hopefully, and they all waited to see who came in.

But it was the vicar of Buckle! The children knew him quite well because he sometimes came to talk to them in their own church at Peterswood. He was a jolly, burly man and they liked him.

‘Can’t be him!’ said Fatty, disappointed. ‘Can’t possibly. Blow! We’re not a bit further on.’

‘Never mind - perhaps one of them will post a letter when they get out of the bus,’ said Pip. ‘We’ll hope for that. Maybe your sour-faced man will, Fatty. He looks the most likely of the lot. He may be telling lies when he says he is a stranger.’

The vicar talked to every one in the bus in his cheerful booming voice. The thin huddled man took no notice, and as the Vicar did not greet him, the children felt sure that he did not know him. So perhaps he was a stranger after all?

‘Soon be at Sheepsale now,’ said Fatty. ‘Golly, isn’t this a steep pull-up? They say it wanted eight horses to pull the coach up in the old days before motor-buses.’

The bus stopped under some big trees in Sheepsale. A babel of baaing, mooing, clucking and quacking came to every one’s ears. The market was in full swing!

‘Quick - hop out first!’ said Fatty to the others. ‘Stand by the post-office - and keep a close watch.’

The children hurried off. Miss Trimble nodded to them and walked away down a little lane. The Find-Outers spotted the post-office at once and went over to it. Fatty produced a letter, and began to stamp it carefully.

‘Don’t want Goon to wonder why we’re all standing about here,’ he murmured to tbe others. ‘May as well post this letter.’

Mrs. Jolly went off to the market to find her sister. The children watched her go.

‘Well, neither Miss Trimble nor Mrs. Jolly have posted letters,’ said Fatty. ‘That lets those two out. Ah - here comes the artist girl.’

The girl smiled at them and went on. Then she suddenly turned back. ‘I see you’ve found the post-office!’ she called. ‘I’m so glad! How silly of me never to have noticed it when I pass it every single Monday. But that’s just like me!’

‘She’s not the one, either,’ said Pip, as she disappeared in the direction of the market. ‘I didn’t think she was. She was too nice.’

The vicar disappeared too, without coming in their direction at all. Now only Mr. Goon and the sour-faced man were left. Mr. Goon stared at Fatty, and Fatty raised his eyebrows and smiled sweetly.

‘Anything I can do for you, Mr. Goon?’

‘What you hanging about here for?’ said the policeman. ‘Funny thing I can’t seem to get rid of you children. Always hanging on my tail, you are.’

‘We were thinking the same thing about you too,’ said Fatty. He watched the sour-faced man, who was standing nearby at the kerb, still reading his paper about dogs and horses. Fatty wondered if he wanted to post a letter, but was waiting till the children and Mr. Goon had gone. Or was he really waiting for his brother, as he had said?

‘There’s the sweet-shop over the road,’ said Fatty, in a low voice, popping his letter into the post-box. ‘Let’s go over there and buy something. We can keep a watch on the post-box all the time. Then if dear old Clear-Orf or the sour-faced fellow are bursting to post letters, they can do it without feeling that we are watching!’

So they all crossed to the sweet-shop and went in. Larry and Daisy started an argument about whether to buy peppermints or toffees, and Fatty watched the post-office carefully through the glass door. He could see, but could not be seen, for it was dark in the little shop.

The sour-faced man folded up his paper and looked up and down the village street. Mr. Goon disappeared into a tobacco shop. Fatty watched breathlessly. There was no one about in the street now - would that man quickly slip a letter into the post-box?

A car drove up. The driver called out a greeting, and the sour-faced man replied. He opened the door and got in beside the driver. Then they drove off quickly. Fatty gave such a heavy sigh that the others looked round.

‘He didn’t post a letter,’ said Fatty. ‘He was telling the truth. Somebody picked him up in a car. Blow! Bother! Dash!’

‘Well, even if he had posted a letter, I don’t see that we could have collared him,’ said Pip. ‘We didn’t know his name or anything about him. But I say - it’s pretty peculiar, isn’t it - not a single one of the passengers posted a letter - and yet one is always posted every single Monday!’

‘Well - we’ll just wait till 11.45 when the post-man comes to collect the letters,’ said Fatty. ‘In case one of the passengers comes back, Ah, there goes Goon, off to the market. I suppose he’s buying butter and cream to make himself a bit fatter!’

The children waited patiently by the post-office till the postman came and took out the letters. Nobody came to post any. It was most disappointing.

‘We’re just where we were! ’ said Fatty gloomily. ‘Sickening, isn’t it? I don’t think we’re such good detectives as we hoped we were! You go off to the market. I want to have a good think. I may get a much better idea soon!’

So off to Sheepsale market went the others, leaving poor Fatty behind, looking extremely gloomy.