No wonder all the girls in the class are disturbed by the newcomer, Mary Beth, who is so much more sophisticated than any of them and whose parents are wealthy.
Every boy is vying for her attention. Even the long-standing friendship of Cecilia and Michael seems threatened when Mary Beth allows Michael, not yet fifteen, to ride her brother's motor scooter, and a scooter is something he wants more than anything in the world.

Before long, however, Michael finds himself involved in a mystery about a series of local thefts. One night he actually witnesses a robbery, makes off with a motor scooter belonging to one of the thieves, and follows them to their hideaway. His daring might have proved fatal except for the curiosity of a dog named Ramrod and the quick action of Cecilia.