In colonial Boston, proud, orphaned, quick-tempered Johnny Tremain works as an apprentice to Mr. Lapham, a master silversmith who is now getting on in years. More clever and skilled than the other two apprentices living at the Laphams', Johnny has the run of the Lapham household. His future seems secure: when he is old enough, Johnny will marry Priscilla Lapham, one of old Mr. Lapham's granddaughters, and inherit the silversmith shop. There he will live out his years, fashioning silver cups and basins and other fine ware for the well-to-do of Boston society.

However, fate or providence has different plans for Johnny Tremain. A crippling accident at the shop leaves Johnny unable to work as a silversmith. He is forced to find other labor, or risk starvation or the gallows. Finally securing employment at The Boston Observer newspaper, Johnny soon finds himself caught up in the on-going struggle between Boston's anti-British Whigs and pro-British Tories. In addition to delivering The Observer throughout Boston and the outlying towns, Johnny begins delivering letters for Sam Adams and The Boston Committee of Correspondence, the secret communications network of the American rebels.

When Boston is occupied by British soldiers in retaliation for the Boston Tea Party, the struggle against England intensifies. Johnny learns from his friend Rab Silsbee and other patriots that both individuals and nations will pay a high price for freedom and independence.

By the close of the novel, Johnny has discovered the secret of his ancestry, he has learned that the Yankees have a fighting chance against the redcoats and he is prepared to take his place among the rebel armies. Johnny has learned, too, that the ideals of the American Revolution must first conquer the human heart before they can conquer armies and empires.