Huck runs into Tom outside of the schoolhouse one day. The two boys discuss the particulars of curing warts, before agreeing to meet up at the graveyard one night, at midnight, in order to try out a new cure involving a dead cat.
While at the graveyard, Huck and Tom watch Injun Joe murder Doctor Robinson, then frame it on Muff Potter. Scared out of their wits, they promise never to tell anyone, write up the promise in a contract, and seal the pact with blood.
Huck, like Tom, feels miserable; he's scared of being killed by Injun Joe, and feels sorry for the wrongfully accused Muff Potter.
Time passes. When Tom and Joe Harper head out to Jackson's Island to become pirates, Huck tags along.
Once there, they play games, swim, etc. They figure out that the people back home think they're dead. Huck gets homesick, as does Joe, but Tom convinces them to stay on and participate in their secret scheme. After weathering a terrible thunderstorm, the boys go back home in time to appear at their own funeral. When no one acts very pleased to see Huck, Tom calls attention to him. Aunt Polly is the first to welcome him back.
Muff Potter's trial begins. At the last minute, Tom testifies against Injun Joe and saves Muff Potter – without mentioning Huck's involvement.
Times passes. Tom decides he wants to go treasure hunting and he enlists Huck to help.
One night, as the boys are exploring a "haunted" house, they are interrupted by the arrival of Injun Joe and a shadowy accomplice.
They watch in silence as Injun Joe finds a big chest of gold coins. When Injun Joe tells his accomplice that they're going to hide it in "No. 2, under the cross," the boys vow to track the treasure down and claim it as their own.
Tom and Huck decide that No. 2 must refer to the number of a room at one of the town's taverns. When Tom sneaks into room number two at the Temperance Tavern and finds Injun Joe sprawled out on the floor, they decide to stake it out.
Huck promises to keep watch every night and to follow anyone who exits the room.
One night, Huck watches two shadowy figures enter the room, then exit carrying a large parcel, which he thinks might be the treasure. He follows them until they stop outside the Widow Douglas's house, where he overhears Injun Joe discussing his plans with his accomplice. When Injun Joe mentions that he's going to attack the widow, Huck runs down to the house of the Welshman, who lives nearby, and asks him for help. Though the Welshman does not trust Huck at first, he comes to believe him. When the Welshman as his sons head out toward the widow's, Huck runs as far away from the area as possible.
The next morning, Huck shows up at the Welshman's and his welcomed with open arms. Huck is told that the men got away.
Huck admits, reluctantly, that one of the men was Injun Joe.
Huck becomes very ill, probably because of stress, and has to be taken care of by the Widow Douglas.
When Tom finally gets out of the cave, he fetches Huck and tells him that he knows where the treasure is hidden.
The two boys go to the cave, find the treasure hidden in a secret underground chamber, and take it out with them.
On their way back to town, they are intercepted by the Welshman, who makes them go to the widow's house with him.
Once there, Huck and Tom are forced to get dressed up. The Widow Douglas has gathered the town's most esteemed citizens for a special meeting. The Welshman tells everyone about how Huck saved the Widow Douglas, and the Widow Douglas tells everyone that, from now on, she will take care of Huck.
At this point, Tom brings in the bags of gold, dumps them on the table, and tells everyone that Huck can take care of himself.
Huck learns how to live like a "normal" person, but he can't stand wearing clothes and going to church, etc.
He runs away from the Widow Douglas.
A few days later, Tom finds him lounging inside of a barrel.
Though he is reluctant to return to the widow's, Tom eventually convinces him to do so, promising that, if he does, and only if he does, he can join Tom's gang of robbers.