Sir Henry Baskerville and Dr Mortimer left the house and walked along Baker steet. Sherlock Holmes watched them through the window of his study.
Quick Watson we must follow them said Holmes
I put on my hat and followed Holmes into the street.
Why are we following them? I asked in surprise.
Because my dear Watson someone else is also following them said Holmes. Look There is the man. There in that cab.
I look where Holmes was pointing. A house drawn cab was moving slowly along the street. A man with a black beard was sitting in the cab. He was watching Sir Henry and Dr Mortimer as they walked towards Oxford Street.