Muff Potter has been accused of the murder of Dr. Robinson. One night, he went along with the doctor and Injun Joe on a grave-robbing expedition at the local cemetery. The men got into an argument, and Injun Joe stabbed Dr. Robinson to death. During the melee, Muff got knocked out, and when he came to, Injun Joe was long gone, leaving him as the only plausible suspect for the doctor's murder.
Fortunately for Muff, Tom and Huck witnessed everything. At first, they're reluctant to come forward and tell the sheriff what happened. They're scared of what Injun Joe might do to them if they spill the beans. But eventually, they realize that Muff's heading for the gallows if they don't confess what they saw that terrible night. So they take the witness stand in the trial of Muff Potter and pin the blame on Injun Joe, who makes a sudden, daring escape, diving through the courthouse window.