The Silent Track Star — Jerry B. Jenkins

This is the seventh book in the adventures of twelve-year-old Dallas O'Neil and his Baker Street Sports Club! You're in for a treat, following Dallas and the gang as they face another puzzling problem. What could be better? One of the fastest runners in the state has moved to Dallas's neighborhood. Everyone in the club is certain he will win a lot of track meets for the Baker Street team. But why is he so quiet? He doesn't seem to have any fun and doesn't seem to want to make any friends. The Baker Street Sports Club learns a tough lesson from him.