The period -- the Revolutionary War; the setting -- Valley Forge; the characters -- a group of sturdy Mennonltes. Johnny, who is about 12, becomes inextricably involved when, with the help of an escaped Negro slave of his own age, he brings supplies to the Army. They enlist the aid of Johnny's elder brother, a soldier, in tracking down a Britisher, posing as friend of the rebels. After a slow start, the story manages to build up high suspense and intrigue. The Old South Theatre in Philadelphia is setting for part of the story which is colorful and dramatic reading.