It was dark when we arrived at Dr Huxtable's famous school in the northern hills. We went quickly into the building out of the cold, and at once someone ran up with news for Dr Huxtable.

"But we need help," said Dr Huxtable. "And I --"

He looked very surprised. "The Duke is here," he told us. "The Duke and Mr Wilder, his secretary, are in my office. Come and meet them."

The Government Minister was a tall man with a long, thin face. He had red hair, and a great red beard. He looked at us, and did not smile. Next to him stood Mr Wilder, a very young man. He was small, with blue eyes, and a watchful face. He spoke first.

"The Duke is surprised, Dr Huxtable, to see Mr Sherlock Holmes here. He doesn't want people to know about this. You know that, so why didn't you speak to the Duke before you went to London?"

"Thank you, sir," said Holmes. "But I would like to stay near to the mystery, here at the school. Can I ask you one or two questions, perhaps?"

"Well," said the Duke. "Mr Holmes is here now, and perhaps he can help us." He looked at Holmes. "I'd like you to come and stay at Holdernesse Hall, Mr Holmes."

"My questions are about the Duchess, and about money," said Holmes.

"I see," said Holmes. "You wrote a letter to your son before he disappeared. When did you post it?"

"Of course," said the Duke.

A minute or two later the Duke and Mr Wilder left. Holmes then began at once to work on the case. We looked carefully all through the boy's bedroom, and the German teacher's room. We looked at the ivy on the wall, and we saw the footprints under the German teacher's window. But we learnt nothing new. Holmes then left the house, and only came back after eleven o'clock.

"The Duchess knows nothing about this," said the Duke, "and nobody is asking me for money."

He had with him a large map. He brought it into my room and put it on the bed.

"This case is beginning to get interesting, Watson," he said. "Look at this map. Here is the school, you see, and here is the road. So, did the boy and the teacher go along the road when they left? No, Watson, they did not!"

"Post it?" said Mr Wilder angrily. "The Duke does not post letters. I put the letter into the postbag, with all the other letters that day."

"How do you know that, Holmes?" I asked.

"Because there was a policeman here -- look. He was there from midnight to six in the morning, and he saw nobody on the road. I spoke to him this evening. And here at the other end, you see, is the White Horse Inn. A woman there was ill, and the family watched the road all night, waiting for the doctor. The doctor didn't come until the morning, and the family saw nobody on the road. So the boy and the teacher did not go by road."

"Yes, Watson, we must remember the bicycle, of course. But first, let's look to the south and the north. To the south we have a big river -- no bicycles there, then. And to the north we have the trees, called Ragged Shaw, and then a great moor, the Lower Gill Moor. And here is Holdernesse Hall, sixteen kilometres from the school by road, but only nine kilometres across the moor. No other houses, until the Green Man Inn, along the Chesterfield road."

"But, Holmes, what about the bicycle?" I asked.

"But the bicycle?" I said again.

"Yes, yes, Watson!" Holmes said. "It is possible to ride a bicycle across the moor -- difficult, but possible."

Just then Dr Huxtable came quickly into the room. "News, Mr Holmes!" he said excitedly. "I bring news!" In his hands was a blue school hat. "Look -- this is the boy's hat. One of my gardeners found it this evening."

"Where, man, where?" asked Holmes.

"Just north of Ragged Shaw," said Dr Huxtable.

"Aha!" said Holmes. "What did I tell you, Watson? Tomorrow we must walk north, across the moor."