In the 1840s an imaginative and mischievous boy named Tom Sawyer lives with his Aunt Polly and his half-brother, Sid, in the Mississippi River town of St. Petersburg, Missouri. After playing hooky from school on Friday and dirtying his clothes in a fight, Tom is made to whitewash the fence as punishment all of the next day. At first, Tom is disheartened by having to forfeit his day off. However, he soon cleverly persuades his friends to trade him small treasures for the privilege of doing his work. He trades the treasures he got by tricking his friends for whitewashing for tickets given out in Sunday school for memorizing Bible verses, which can be used to claim a Bible as a prize. He received enough tickets to be given the Bible. However, he loses much of his glory when, in response to a question to show off his knowledge, he incorrectly answers that the first disciples were David and Goliath.

Tom falls in love with Becky Thatcher, a new girl in town, and persuades her to get "engaged" by kissing him. Becky kisses Tom, but their romance collapses when she learns that Tom has been "engaged" previously—to a girl named Amy Lawrence. Shortly after being shunned by Becky, Tom accompanies Huckleberry Finn, the son of the town drunk, to the graveyard at night to try out a "cure" for warts with a dead cat. At the graveyard, they witness the murder of young Dr. Robinson by Injun Joe. Scared, Tom and Huck run away and swear a blood oath not to tell anyone what they have seen. Injun Joe frames his companion, Muff Potter, a helpless drunk, for the crime. Potter is wrongfully arrested, and Tom's anxiety and guilt begin to grow.