In revolutionary Boston, Johnny Tremain is an apprentice in the household of Mr. Lapham, an old master silversmith who lives with a daughter-in-law, Mrs. Lapham, and his four grandchildren: Madge, Dorcas, Cilla, and Isannah. Johnny serves with two other apprentice boys, Dove and Dusty. Johnny is the most skilled of the three, so he is able to boss the other two around. Old and pious Mr. Lapham tries to teach Johnny to be humble according to the bible, but Johnny is prideful because he knows the shop cannot function without him.
One day, John Hancock, the richest man in Boston, stops by with an order for a silver sugar basin. Johnny is consumed with making the basin handle, even going to Paul Revere for advice. But because he continues to be demanding on the other boys, Mr. Lapham stops work, jeopardizing the timely completion of the project. So Mrs. Lapham arranges for Johnny to work illegally during the Sabbath. But Dove, in order to teach Johnny a lesson, hands him a cracked crucible, which results in a horrible accident where Johnny's thumb becomes attached to his hand, promptly ending his career as a silversmith apprentice.
Mr. Lapham pledges to keep Johnny around, but tells him he must find another line of work. Mrs. Lapham, who once depended so much on Johnny, now finds him to be a burden. Johnny falls out of favor with her and so he no longer feels wanted. Mrs. Lapham even arranges for a journeyman silversmith, Mr. Tweedie, to partner with Mr. Lapham.
Johnny tries to find work in various trades, even going to John Hancock, but no one will take him because of his bad hand. Johnny reaches his emotional bottom when Isannah refuses to be touched by his hand. Johnny heads to his mother's grave and breaks down. There, he decides to go see Jonathan Lyte, a rich merchant and possible kin. Before she died, his mother had told him to go to his rich relative only if there were no other choice. She gives Johnny a silver cup as proof of his claim in the Lyte family (the only person who knows about the cup is Cilla).
Before Johnny heads to Merchant Lyte, he enters a printing shop of the Boston Observer, a pro-independence newspaper. Johnny meets an intriguing boy slightly older than him named Rab. Rab, whose uncle runs the printing shop, has a quiet confidence about him that Johnny admires. Johnny tells Rab about his situation, and Rab offers him a job as a rider.
When Johnny goes to Jonathan Lyte, the merchant kicks him out. But when he finds out about Johnny's cup, he asks to see it. Johnny tells Rab about his visit to Merchant Lyte and finds out that Merchant Lyte is crooked. When Johnny takes his cup, Merchant Lyte accuses him of stealing it and has him arrested. With the help of Rab and through Cilla's testimony, Johnny is freed. He then takes up Rab's offer to be a rider for the Boston Observer.
Johnny's new life as a rider of the Boston Observer allows him access to the main leaders of the American Revolution, such as Sam Adams, Paul Revere, John Hancock, Doctor Warren, and James Otis. Johnny takes part in the Boston Tea Party, and uses his skills to spy against the British. And through his friendship with Rab and Cilla, Johnny begins to mature and develop as a person.
As American protest intensifies, Johnny learns from Miss Lavinia Lyte, the daughter of Merchant Lyte, that he is his grandnephew. Although Johnny learns about his past, he realizes he must put it aside and live for the future, just as America seeks to break from its British heritage and forge a new identity.
As war nears, Rab, who is from Lexington, decides to join the Minute Men there. When the first British troops start moving, Johnny is there to relay the message to Paul Revere, who makes his historical midnight ride throughout the countryside to warn the Minute Men. At the Battle of Lexington, Rab is wounded, and eventually dies. Johnny is crushed, but he knows that many young men must die to achieve the goal of liberty and freedom. He learns from Doctor Warren that his thumb can be freed. Johnny agrees to undergo surgery so that he can take up Rab's musket and continue the fight for independence-in order "that a man can stand up."
