One day ,I happened to(碰巧)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 Chicago was a very big city. He was silent(沉默)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 eourt(网球场). He added that he knew a lot of people with swimming pools, but that he only knew two people in the country 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 neighbour. I said that my brother was a doctor. The doctor had a tennis court. I told him that my next door neighbour 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 people does the story involve(涉及)?