A whirligig is something that has one or more pieces which spin around in the wind. In this story, the main character builds whirligigs to repay a mother whose child has died in a car accident.
Mostly, Brent is the character who changes. He begins the book as a self-centered boy who is desperately trying to fit in by having the right clothes, car, music, and enough money to spend. After the car accident in which a girl dies, everything about him changes.
Brent takes a lot of trips--bus rides, meeting strangers, camping, making whirligigs--and he learns a lot with each one. Through his learning about himself and his life, the reader has the opportunity to re-examine his/her own life and priorities as well. The purpose of the trips is at the request of the girl's mother. She has asked that he travel to the four corners of the USA to put up whirligigs which display her daughter's face. After he has complete his mission, he returns home, changed forever.
Other characters are background characters that lend support to Brent and his amazing character metamorphosis.