It had just struck ten next morning when Dr Mortimer and Sir Henry Baskerville knocked at the door of the house in Baker Street.
The latter was a short dark-eyed man of about thirty with a sunburnt, energetic face. In his hand he was holding an envelope.
"This is Sir Henry Baskerville," said Dr Mortimer.
"Yes," he said, "and the strange thing is, Mr Holmes, that if my friend had not suggested coming round to see you this morning I should have come anyhow. I know that you solve little puzzles, and I've had one this morning that I cannot solve.
I have just received a strange letter and I want to show it to you."
He laid the envelope on the table. The address "Sir Henry Baskerville, Northumberland Hotel" was written in capital letters.
"Who knew the address of your hotel?" asked Holmes quickly.
"No one could have known it, because I decided to go there only after I had met Dr Mortimer."
"Really? Somebody is very much interested in you," said Holmes. He opened the envelope and took a large sheet of paper. There was only one sentence formed of printed words stuck upon the paper. "If you value your life, keep away from the moor." Only the word "moor" was written in ink.
"Now," said Sir Henry Baskerville, "perhaps you will tell me, Mr Holmes, what all this means?"
"This interesting document was written and posted yesterday," said Holmes, looking at the stamp. "Have you yesterday's copy of The Times, Watson?"
"Here it is," said my friend, giving me the newspaper.
Holmes glanced swiftly over the leading article and soon found where the words of the strange letter had been taken from.
"Someone has cut out these words and stuck them on the paper," said Holmes. "The word 'moor' was written in ink, because it couldn't be found in the newspaper. It's less usual than the other words of this sentence. You can see that some words are stuck much higher than others. It shows that the writer of the letter was in a hurry, or perhaps he was afraid that somebody might see him. And now, Sir Henry, has anything else happened since your arrival in London?"
"No, Mr Holmes, I think not."
"Are you sure that nobody follows you or watches you?"
"Why do you ask me such strange questions, Mr Holmes? Do you know anything that I don't know?"
"You will hear everything before you leave this room, Sir Henry. I promise you that," said Holmes. "But first I want to know about the smallest incidents that have taken place since you came to London, anything unusual for everyday life."
"Well, I don't know much about British life yet. I have spent nearly all my time in America and Canada. But I hope that to lose one of your boots is not part of everyday life here in Britain," said Sir Henry with a smile.
"Have you lost one of your boots?"
"Yes. I only bought this pair of boots last night and I haven't even worn them."
"And you think that one of them was stolen?"
"This is very strange," said Sherlock Holmes, "But I hope that this missing boot will soon be found. And now, Dr Mortimer,
you must tell your story to Sir Henry as you told it to us."
Sir Henry Baskerville listened to Dr Mortimer's story with great attention and with exclamations of surprise.
"Of course I've heard of the hound," he said. "When I was quite a small child, my parents often spoke of this legend, but nobody thought of it seriously. However the death of my uncle and the letter which I received this morning are very strange."
"How do you think to act?" asked Holmes. "Will you go to Baskerville Hall?"
"The moor is a dangerous place," said Dr Mortimer.
"I have firmly decided to go to the home of my own family," answered Baskerville. "No devil in hell or man upon earth can prevent me from going there. But it's half past eleven, Mr Holmes, and I'm going back to my hotel. If you and your friend Dr Watson can come and have lunch with me at two o'clock we'll speak more about this matter."
"We'll certainly come," said Holmes shaking hands with his two visitors. As soon as they were in the street he jumped up and cried: "Your hat, Watson, quick! There's not a moment to lose. We must follow them."
We ran down the stairs and into the street. Dr Mortimer and Sir Henry were walking in the direction of Oxford Street about two hundred yards ahead of us.
"Shall I run and stop them?" I asked.
"Oh no, my dear Watson," answered Holmes, "this will spoil all my plans. They mustn't know that we are following them."
At the corner of Regent Street Dr Mortimer and his friend stopped before the window of a shop and at the same moment Holmes gave a little cry of satisfaction.
"Look, Watson,' he whispered, pointing to a cab that had also stopped on the other side of the street. There was a man in it with a thick black beard and a pair of piercing eyes. He was watching Sir Henry. Suddenly his eyes turned towards us. In a moment he had closed the window of the cab, and it moved forward quickly. Holmes looked round for another, but there was not a cab in sight. So the man with the black beard was soon far away.
Dr Mortimer and Sir Henry continued their way. They didn't know that a stranger had been following them.
"Who was that man?" I asked.
"I don't know, but I'm sure he knew that Sir Henry was at the Northumerland Hotel. This means that he has followed our young friend from the moment he came to London. So I decided to follow Sir Henry myself, hoping to catch the spy."
"But why did he take a cab?"
"Because he was prepared to follow our friends in case they took a cab."
"What a pity we don't know the number of the cab," I said.
"My dear Watson, it's 2704. Now come along. The spy has gone and will not return. Let us visit one of the picture galleries to fill in the time before lunch. It's 12 o'clock now and Sir Henry doesn't expect us till 2."