A mischievous boy growing up in a Mississippi River town in the 19th century impresses his friends and horrifies adults by associating with the son of the town drunk, running away from home, attending his own funeral, etc.
Tom arrives at school late and finds that Becky is in his class. He finally manages to become friends with her, and promises to visit – forgetting another promise he has made to Huck.
Muff is arrested for the murder, just as Indian Joe planned. Tom and Huck sympathize with Muff and send in food and cigarettes, but keep their silence. Tom is plagued by nightmares.
Tom distributes handbills in return for the medicine. It sells like hotcakes, then the two men disappear. The medicine turns out to be a sham. Tom doesn't get the mumps, but he makes many trips to the outhouse.
The villagers believe the boys have drowned in the river. Though they play all day on the island, Ben misses his home. Tom returns secretly for news of the village and sees Aunt Polly praying for his safety.
A large steamship comes to St Petersburg. Tom and Huck steal aboard for a trip. Next day, Tom boasts about their adventure, fascinating his classmates.
Tom and Huck reach Aunt Sally's ranch safely and hand over the papers. Tom introduces Huck as his brother Sid. While out riding, they spy a white horse.
Tom discovers a dead body up the river, it appears to be Huck's father! After the funeral, Huck's father appears alive and comes to take his son. Huck doesn't want to go and hides.
After the funeral, Tom is a hero at school, and everyone wants to hear his story. Charlie inks Tom's schoolbook out of jealousy, and Tom is punished. Becky saw what happened and feels guilty that she did not tell the truth.
Tom Sawyer doesn't like school much. Escaping from the schoolhouse, he's off to the woods to catch a wild pig with his friend Huck. Their attempts to sell the pig at the harbor end with a wild disturbance on the steamboat.
Tom just can't get along with his new classmate Alfred, and challenges him to a fighting match. On the way home, the boat they are aboard sinks and Tom rescues Alfred, who can't swim at all – winning Becky's praise.
Tom and Huck have a grand time on the ranch. When the ranch hands decide to catch the white horse named Lightning, the boys go along. The horse is finally captured, but Tom feels they have injured Lightning's pride.
Tom and Huck suffer from their guilty consciences and decide to tell the truth. Indian Joe comes to the trial with confidence, but Tom's testimony foils his plan. Joe takes flight and Muff is declared not guilty. Tom is again the children's hero.
Tom gives Becky an engagement kiss. But with a slip of the tongue, he tells her that he had once been engaged to Amy. Becky is furious, and Tom becomes so discouraged he ends his treasure hunt.
Aunt Polly falls sick and is struck with an idea. She calls Tom to her bedside, pretending to be dying. Aunt Polly tells Tom she cannot go to heaven unless he promises to be a good boy but Tom refuses to promise, because he doesn't want his aunt to die.
Huck is offended that Tom forgot his promise. The next few days Tom works with Huck, telling Becky he is busy helping his sick aunt. Becky discovers his lie but her anger is replaced with surprise when she sees Huck's newly built tree house.
Tom is dismayed when Aunt Polly tells him he must spend his Saturday whitewashing the fence. Too long to paint in one day, Tom convinces his friends of the joys of the job, and soon has all the help he needs.
On their way to a haunted house in the middle of the night, Tom and Huck witness a murder. Indian Joe kills Dr. Robinson, then lays the blame on Muff Potter. Tom and Huck exchange a promise to keep their secret because they fear Indian Joe.
Alfred hones his swimming skills in order to show up Tom. At his birthday party, he challenges Tom to a swimming race and wins. Tom then challenges Alfred to a contest to see who can stay under the water the longest.