The day of Muff Potter’s trial approaches, and Tom lives in constant fear. Whenever people bring up the murder, he feels guilty and wonders if they are trying to make him confess something. He knows that nobody can know that he witnessed the crime, but he is in an agony of guilt. He finds Huck in a similar condition, and the two of them go off to a quiet spot to talk.

Tom and Huck feel badly for Potter. The man “ain’t no account,” but he is kind. When he was free, he sometimes shared food with Huck even when he did not have enough for himself. He was also nice to Tom, helping him mend kites and put hooks onto fishing lines. Both boys wish they could find a way to free Potter, but they know that the townspeople would lynch him if he escaped. They remain afraid of what Injun Joe would do to them if they told the truth, so they renew their commitment to “keep mum” about the murder.

The boys feel guilty about their decision, so they often bring Potter tobacco and matches in the prison. Today when they stop by his cell, they end up feeling guiltier than ever. Potter praises both boys for standing by him when the rest of the townspeople have turned their backs. He says that it is right for him to be hung for his crime, and he asks the boys to promise never to turn to drink, in case they end up like him. That night, Tom cannot sleep.

Tom goes to the trial and listens to each witness giving testimony. The prosecutor calls witnesses to describe Potter’s suspicious behavior on the night of the murder, to identify his knife, and so on. Each time the prosecutor finishes the witness, Potter’s lawyer says that he has no questions. By the third or fourth time this happens, the crowd begins to murmur. Except for Tom, Huck, and Injun Joe, everyone is convinced that Potter is guilty. Still, they want his lawyer to try, at least, to mount a defense.

When the prosecution rests its case, Potter moans, believing his death sentence is near. However, his lawyer surprises him and everyone by calling Tom Sawyer to the witness stand. Tom rises and walks fearfully forward. He takes the oath to tell the truth. When asked where he was at the time of the murder, Tom glances at Injun Joe. At first he is too afraid to speak, but he knows he has to tell the truth now. He whispers that he was in the graveyard.

As Tom tells his story, he slowly gains confidence. The crowd goes silent, listening with rapt attention. Just as Tom is about to reveal the identity of the murderer, Injun Joe leaps from his seat and springs out the window.