Fourteen-year-old Johnny Tremain is the gifted apprentice of Ephraim Lapham, a silversmith in Revolutionary-era Boston. The pious and elderly Mr. Lapham is more interested in preparing his own soul for death than in running his silver shop, so Johnny is the chief breadwinner of the family. Dove and Dusty, Lapham’s other apprentices, are expected to bow to Johnny’s authority, and Mrs. Lapham is determined to have Johnny marry her daughter Cilla. Johnny’s enormous talent and his special status in the Lapham household go to his head, and Johnny often bullies the lazy, insolent Dove, as well as Dusty and the four Lapham daughters. Although Mr. Lapham tries to contain Johnny’s arrogance, Johnny is unwilling to rein in his quick temper or impulsive acts.

The Lapham’s fortune and Johnny’s fame as a silversmith appear to take a turn for the better when the wealthy merchant John Hancock puts in an order for an elaborate silver basin. Mr. Lapham hesitates to take on such a difficult project, but the rash Johnny accepts the job on behalf of his master. That night, Johnny reveals his family secret to Cilla. He is related to Jonathan Lyte, a wealthy Boston merchant. Johnny’s mother revealed his ancestry to him before she died and gave him a silver cup engraved with the Lyte’s coat of arms. She instructed him to steer clear of the Lytes unless he had no other recourse.

Johnny struggles to design the silver basin’s handles, but he is dissatisfied with the result. After consulting Paul Revere, Johnny creates a mold for a perfect set of handles. While he is casting the wax model in silver, Dove deliberately hands him a cracked crucible. Dove’s intention is only to humble Johnny by playing a practical joke on him, but his prank results in a terrible accident that disfigures Johnny’s hand. No longer able to work as a silversmith’s apprentice, Johnny loses his status in the Lapham household. After the burn heals, Mrs. Lapham begins to complain of Johnny’s idleness and the expense of feeding him. She begins negotiating a business partnership with Mr. Tweedie, a silversmith from Baltimore, and forbids Johnny from marrying Cilla. Mr. Lapham urges Johnny to find a new trade, but promises to house him until he finds a new master. During his fruitless search, Johnny drops into Mr. Lorne’s print shop, where a Whig newspaper, the Boston Observer, is published. Mr. Lorne’s enigmatic nephew and apprentice Rab immediately intrigues Johnny. Johnny confides the story of his accident to Rab, and the boy promises Johnny a job delivering newspapers if he fails to find any skilled labor.

Depressed and desperately trying to find a new craft, Johnny finally decides to approach Jonathan Lyte. He produces his silver cup as proof of their kinship, but Lyte accuses Johnny of stealing the valuable heirloom and has the boy arrested. Johnny appeals to Rab for assistance, and Rab not only finds a lawyer to defend him for free but also arranges to have Cilla testify in his favor. After Johnny is cleared of the charges, he tries to sell the cup to Lyte, but Lyte steals it from him. Only then does Johnny approach Lorne to ask for the delivery job.

While delivering newspapers, Johnny becomes well acquainted with the key members in Boston politics and is transformed from an apathetic political bystander into an ardent Whig. The Lornes treat him kindly, as if he were a member of their family. Johnny participates in the Boston Tea Party, and becomes a confidant, small-time Whig spy, and errand boy for all the Whigs of Boston. During this period of Whig scheming, in the months leading up the Revolutionary War, Johnny slowly changes from a selfish, arrogant child into a selfless, idealistic man. Rab’s quiet influence teaches Johnny to control his temper, and the colonial situation provides Johnny with something larger than himself to care about. Johnny also matures through his growing recognition of his feelings for Cilla, who has gone to work as a servant in the Lyte home.

On the eve of war between the colonists and Britain, the Tory Lytes plan to flee to England. Immediately before their departure, Lavinia Lyte approaches Johnny to tell him that she has investigated his claims of kinship and found them to be legitimate. She insists that her father had sincerely believed that Johnny was lying when he accused him, but admits that both father and daughter recognize that Johnny has a right to some of the Lyte property.

Rab is mortally wounded when war breaks out in the battle of Lexington. Johnny is deeply shaken by Rab’s death, but he vows to continue the struggle for the human rights for which Rab sacrificed his life. Doctor Warren, an esteemed rebel leader, examines Johnny’s hand while Rab’s lifeless body lies upstairs. He discovers that the thumb is fused to the palm by nothing but scar tissue, and that Johnny’s handicap can be easily remedied with minor surgery. Although he cannot promise that Johnny will ever be a silversmith again, he assures Johnny that he will soon be able to fire the musket that Rab bequeathed to him before dying.