One day, I happened to talk to a stranger   on the bus. When he found out that I was from Chicago, he told me that one of his good friends lived there and he wondered if I happened to know him. At first I wanted to say that it was foolish   to think like that, for from all the millions of people in Chicago, I could not possibly know his friend. But, instead, I just smiled and said that Chicago was a very big city. He was quiet for a few minutes, and then he began to tell me all about his friend. He told me that his friend was an excellent tennis player and that he even had his own tennis court  . He added that he knew a lot of people with swimming pools, but that he only knew two people in the country who had their own tennis courts. And his friend in Chicago was one of them. I told him that I knew several people like that, for example, my brother and my next-door neighbor. I told him that my brother was a doctor and he lived in California. Then he asked where my brother lived in California. When I said Sacramento, he said that last year his friend spent the summer in Sacramento and lived next door to a doctor. The doctor had a tennis court. I said that my next-door went to Sacramento last summer and lived in the house next to my brother's. For a moment, we looked at each other, but we did not say anything. "Would your friend's name happen to be Roland Kirkwood?" I asked finally. He laughed and said, "Would your brother's name happen to be Dr. Ray Hunter?" It was my turn to laugh. How many persons does the story involve  ?
Four. Five. Six. Seven.