"Come, Watson," he cried. "There is hot coffee ready for you. We leave in ten minutes."

Very early the next morning I opened my eyes, and saw Holmes next to my bed. He was already dressed.

"We can easily see tracks in this wet ground," said Holmes. "Look carefully, Watson!"

By six o'clock we were through Ragged Shaw, and half an hour later we were on Lower Gill Moor. Across the middle of the moor was a small river, and the ground all around it was very wet.

"Hurrah!" I cried. "We have it."

But Holmes did not look happy. "It's a bicycle, yes, but not the bicycle. Every bicycle has different tyres -- I know forty-two different kinds of tyre. This tyre is a Dunlop, but Heidegger's bicycle had Palmer tyres. The English teacher told me that. So this is not Heidegger."

We moved slowly across the moor, looking at every centimetre of mud. We found hundreds of sheep tracks, and once some cow tracks -- but no bicycle tracks. And then at last, we found something. Not far from the little river, right across some nice black mud, was the track of a bicycle.

"Probably not. The boy didn't take a bicycle with him," said Holmes. He looked again at the track in the mud. "This track is going away from the school."

"Is it the boy, then?" I asked.

"Er, no," I said. "One tyre makes a deeper track."

"Or perhaps to the school?" I said.

"No," he said, getting up. "We must leave this question for now. Back to the mud by the river, Watson!"

Two hours later Holmes gave a happy cry. I quickly ran over to him, and looked down at a long thin track in the mud. It was the Palmer tyre.

"No, no, my dear Watson. Look at the tracks of the two tyres. Are they the same?"

"And that's the back wheel," said Holmes, "because the rider, of course, sits over the back wheel. The deeper track is the one on top, so this bicycle went that way, across the moor away from the school. But who was the rider? Where did he come from?"

We followed the Dunlop track back, nearly to Ragged Shaw. Then we lost it, in some cow tracks. Holmes sat down and thought for some minutes.

We soon found the bicycle, and then behind a bush we saw a shoe, and found a body. There was blood on the man's head and face, and he was very, very dead. He had shoes on, but no socks, and we saw a night-shirt under his open coat. It was the German teacher.

"Here is Heidegger!" cried Holmes. "Let's follow him, Watson."

"What happened here?" I said. "Did he fall?"

On one of the yellow flowers there was something red -- the dark, browny-red of blood.

For a kilometre or more we followed the Palmer tyre north across the moor, losing the track, finding it again, losing it, and finding it. Suddenly, the track stopped.

Holmes looked carefully on the ground. Then he moved to some small bushes with yellow flowers on them. "Look," he said quietly.

"Bad!" said Holmes. "Bad! What do I read here? Something or someone hit him. He fell, he stood up, he got onto his bicycle again, and rode away. But there is no other track. Some cow tracks here, but no footprints. We must follow the blood, Watson."

"Poor man," Holmes said quietly. "What shall we do, Watson? We can't lose any more time, but we must tell someone about this poor man."

"Shall I run back to the school?" I said.

"No, I need you with me." Holmes stood up and looked around. "Look!" he said. "There's a workman over there. He can go back to the school for us."

I went and got the workman, and Holmes wrote a note for Dr Huxtable. The poor workman took one look at the body, and began to run quickly down the hill to Ragged Shaw.

"That's right," I said.

"Now," said Holmes, "before we go on, let's think carefully for a minute. What do we know so far? First, the boy left freely. He was dressed, he did not leave suddenly, he wanted to go -- perhaps with someone, perhaps not. But the German teacher left without his socks and without his shirt, so he left very suddenly."

"And why did Heidegger go? Because, from his bedroom window, he saw the boy. Because he wanted to follow him and bring him back. So far, so good. But why doesn't Heidegger just run after the boy? A man can easily run faster than a boy -- but Heidegger doesn't do this. He gets his bicycle. He knows that he needs his bicycle. Why?"

"Ah," I said, "because the boy has a bicycle."

"Holmes," I cried. "This is not possible."

"Very good, Watson," he said. "It's not possible, so something is wrong with my thinking. What can it be?"

"Perhaps," I said, "Heidegger broke his head in a fall?"

"Not so fast, Watson. Think about it. Heidegger dies eight kilometres from the school. So the boy is moving very fast, because it is eight kilometres before a man on a bicycle can get near him. And Heidegger dies because someone hits him very hard on the head. A boy can't do that, so there was someone with the boy -- a man, let's say. But we looked very carefully at the mud all round poor Heidegger's body, Watson, and what did we find? Some cow tracks, but nothing more. No footprints from people, no bicycle tracks."

"In mud, Watson?"

"Oh, I don't know, I just don't know."

"Come, come, Watson," said Holmes. "Every mystery has an answer. But for now, the Palmer tyre can tell us nothing more, so we must go back to the Dunlop tyre."

We found the Dunlop track again and followed it north. Here there was very little mud, and we lost the track. Across the moor we could now see Holdernesse Hall, some kilometres to our left, and in front of us we could see the Chesterfield road. We walked down to the road, and along to the Green Man Inn.