Johnny Tremain is a self-confident, tempestuous 14-year-old apprentice who has assumed control of the silversmith shop where he works. But when Johnny injures his hand, his dreams of becoming a silversmith fade. He tries to prove he is related to a wealthy Boston merchant, but the merchant spurns him and accuses him of theft. As Johnny gradually begins to mature, he learns to control his temper and think past his own self-interest. With the help of his friend Rab, he joins the ranks of colonists resisting British rule, and he participates in the events leading to the start of the American Revolution.
Rab Silsbee works for his uncle, who publishes the Boston Observer newspaper. After Johnny hurts his hand and loses his place at the silversmith's, Rab helps him get back on his feet and learn to control his arrogance. Rab is a member of the Sons of Liberty, a secret group that advanced the rights of colonists and fought against taxation by the British government. Rab helps Johnny become involved in revolutionary activities as well. Rab has family in Lexington. He leaves Johnny behind in Boston when the British soldiers begin their march on the countryside and the American militia mobilizes to stop them. The subsequent fighting leads to his death.
Cilla Lapham has the often thankless job of caring for her younger sister, the precocious Isannah. When Lavinia Lyte takes Isannah into her home, Cilla goes along as a maid. Cilla remains devoted to Isannah no matter how poorly Isannah treats her in return. While Johnny is the top apprentice in Mr. Lapham's silversmith shop, he teases Cilla. After he hurts his hand and is arrested for theft, Cilla's testimony gets him acquitted, and he begins to see her in a new light, finding new respect and affection for her.
The legendary silversmith and horseman is a friend to Johnny. He first offers Johnny advice about repairing silver pieces, and later he acts as Johnny's revolutionary mentor. Johnny helps Revere before his historic ride into the countryside to warn the colonial militia of the British troops' advance.
Somewhat of a failure as a businessman, Sam Adams is a genius at leading the revolutionary movement against British rule in colonial New England. Johnny thinks that if the British had a chance to capture and execute any of the leaders of the Boston Observers, it would be Sam Adams and John Hancock.
Jonathan Lyte is one of the wealthiest men in Boston. While pretending to be on the side of the colonists, he often works slyly to find a way around their boycott of British goods. When Johnny—accurately—claims to be related to him, Lyte not only denies this but also falsely accuses the boy of theft and has him thrown into jail. In ill health, Lyte moves his family to his estate outside Boston to escape the growing tensions between colonists and the British. But colonists attack his mansion, driving his family back to the security of the city.