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.

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 and Huck suffer from their guilty consciences and decide to tell the truth. Indian Joe comes to the trial with confidence, but Toms testimony foils his plan. Joe takes flight and Muff is declared not guilty. Tom is again the childrens hero.

The sheriff calls in a detective from St. Louis to find Indian Joe, but to everyone's disappointment, he is unsuccessful. He is sure, however, that Joe will seek revenge. The detective follows Tom continually, hoping eventually to arrest Indian Joe.

Aunt Polly asks Tom to visit Aunt Sally in Arkansas and deliver important papers. Glad to go as Becky is also traveling to St. Louis, and the trip will keep him away from Indian Joe. To the surprise of Tom and Becky, Huck steals aboard the steamship.

Tom and Huck reach Aunt Sallys ranch safely and hand over the papers. Tom introduces Huck as his brother Sid. While out riding, they spy a white horse.

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 Lightnings pride.

Bennie discovers that Huck is not Toms brother, but offers to keep their secret in return for help. The ranchers try to tame Lightning, but the Indians say they should release the horse. Out of love for Lightning, Bennie releases it with Tom and Huck.

Tom sneaks out to go to the haunted house with Huck. There they learn that Indian Joe has come back to the village in disguise. By chance, Joe and his friend find a box of gold coins. Tom informs the sheriff but is not believed.

All the children go on a picnic except Sid, who has a cold, and Huck. Tom and Becky get lost while exploring a cave. Trying to find the way out, Tom sees Indian Joe coming in. Huck discovers Joes friend, killed.

A search party forms to find Tom and Becky. Indian Joe comes upon Tom and scares him, but does no harm. Pursued by the sheriff, Joe falls into a gorge and meets his end. Tom, to his surprise, feels sorry for Joe. Later, Tom and Huck find gold coins.

The judge divides the gold between Tom and Huck. Mrs. Douglas is chosen as Hucks guardian, and he begins a new life under strict discipline. A new school year begins, and Huck attends with Tom. On day one, the two are in trouble with the new teacher.