Because he is looking forward to spending the lunch hour with Becky, Tom cannot concentrate on his book. He takes out a tick he has captured, and he and his friend Joe Harper begin to drive and control the tick by prodding it with pins. To try to introduce some order, Tom draws a line down the middle of his slate, puts the tick on the slate, and tells Joe that as long as the tick is on Joe's side, Joe can control the tick, whereas when it is on Tom's side, only Tom can control it. At last, Tom, unable to restrain himself, interferes with the tick when it is on Joe's side, and the two boys begin to argue. The teacher's attention is caught and both boys get a whipping.
In the lunch hour, Tom meets Becky in the empty schoolroom and teaches her to draw. Tom persuades Becky to tell him that she loves him and to get "engaged" to him, which means, he says, that she will never have anyone else but him. In his excitement, Tom begins to talk about how wonderful being engaged is, and lets slip that he was previously "engaged" to Amy Lawrence. Becky starts to cry, saying that he must still love Amy, and pushes him away. Tom denies that he cares for anyone except Becky. He offers her his best treasure, a brass knob from a fire iron, but she strikes it to the floor. Tom marches out of the school. Becky tries to call him back, but he is gone, and she has no one to share her grief.
Tom wanders off into the woods, nursing his sadness and anger at Becky's treatment of him. He fantasises about dying or running away to join the army, and thinks how sorry she would be. Finally, he settles on running away to become a pirate.
He digs under a log and retrieves a treasure box that he had buried there two weeks previously. Tom had placed a marble in it and said various incantations over it, in the superstitious belief that when he dug it up, all the marbles he had ever lost would have gathered themselves around it. But the charm has not worked - there is still only the solitary marble in the box - and Tom concludes that "some witch had interfered and broken the charm." He uncovers a doodle-bug and asks it whether his supposition is correct, but naturally, the doodle-bug does not reply. This confirms Tom's suspicion that a witch is reponsible, and has terrified the bug into silence.
Tom meets Joe Harper, and they play at Robin Hood before going home. They agree that "they would rather be outlaws a year in Sherwood Forest than President of the United States for ever."
That night, Tom is in bed when he hears a noise like a wailing cat. It is Huck, who has brought his dead cat and making the sign for Tom to come out and go with him to the graveyard, where they plan to try out the wart charm. Tom escapes through the window and the boys go to the graveyard, where they hide themselves and wait for the devil to appear.
Soon, three figures appear. The boys at first think they are devils, but then they realize that they are Dr Robinson and two local outcasts, Muff Potter and Injun Joe. Muff Potter is drunk. Dr Robinson leads the men to the grave of Hoss Williams and tells them to dig up the corpse, presumably for medical experiments. They do so, and load the corpse onto a barrow, but Potter refuses to let the doctor take it unless he pays them extra money. Dr Robinson protests that he has paid them already. Injun Joe joins Potter in threatening Dr Robinson. He says that five years ago Dr Robinson had driven Injun Joe away when he had come begging to his house, and then the doctor's father had jailed him as a vagrant. Now, Injun Joe wants revenge.
Dr Robinson strikes Injun Joe, who falls to the ground. Potter drops his knife and grapples with the doctor. Injun Joe gets up and snatches up Potter's knife. Dr Robinson seizes the headboard from Hoss's grave and fells Potter with it, at which Joe stabs Dr Robinson in the chest. The doctor falls on top of Potter, covering him with blood. Tom and Huck are terrified. They run away, unseen by the men.
The doctor dies. Joe robs the body and puts the knife in Potter's hand. When Potter regains consciousness, he realizes that he is holding a knife and drops it with a shudder. He sees the doctor's body and asks Injun Joe if it is true that he, Potter, killed him. Joe replies that the doctor hit Potter with the headboard, and that Potter stabbed the doctor just as the doctor was hitting him again. Both Both fell to the ground, Joe says. Potter is confused, as he has never used weapons, but he concludes that he must have been carried away by the whiskey and believes Joe's story. Joe agrees not to tell anyone what happened, and Potter leaves. Joe, pleased to see that Potter has left his knife at the scene of the crime, leaves separately.
Analysis of Chapters 7-9
Tom's interactions with Becky show that, while he is ahead of his classmates in being interested in girls, he is still immature when it comes to dealing with emotions. He has a strong romantic imagination and can place himself in exciting narratives with ease, to the extent of recreating the dialog from stories he has heard or read. His mistake is to bring his games of makebelieve into his relationship with Becky, with unhappy results. Carried away by a romantic fantasy, he persuades her to get "engaged" to him, but in his excitement, blurts out that he was previously "engaged" to Amy Lawrence. When Becky cries, he cannot deal with the situation. Instead, he escapes into the woods and takes refuge in his fantasies of running away to become a pirate, and pretending to be Robin Hood.
Tom's choice of fantasy - that of becoming a pirate - is significant. To Tom, a pirate unites freedom with fame, but is mercifully free of responsibility or any awareness of consequences to actions. Tom's fascination with superstitions, such as his faith that a buried marble will somehow attract all his other lost marbles, has a similar basis in irresponsibility: unwilling to accept that the only solution to lost marbles is to do the hard work of looking for them or to take care not to lose them in the first place, Tom wants them magically to return in response to his charm. It is no surprise that the charm fails, but in seeking to blame a witch even for this, Tom still avoids facing the harsh truth - that he lost the marbles, and that they remain lost. However, responsibility and an awareness of consequences are exactly the lessons he is about to learn, the hard way.
The incident of the murder in the graveyard shifts the narrative, and the moral tone, to a different level. While Tom has always got into trouble, his activities have been harmless and have had no consequences. Now, he and Huck are witnesses to the murder and framing of an innocent man (Potter). Depending on what they do, or fail to do, an innocent man could be hung and the real murderer escape justice.
Injun Joe is presented as such an unregenerate villain that it is hard to feel any sympathy for him. The depth of his evil is shown by his eagerness to kill Dr Robinson in revenge for a relatively small offense, the doctor having driven him away when he came begging to their house and the doctor's father having him put in jail for vagrancy. Not only is he a murderer, but he pins the crime on an innocent man who trusts him. As a result, Potter risks being hanged.
Many readers will see the character of Injun Joe as a racist portrayal of a half-Indian man, called by Twain a "half-breed." This interpretation is supported by Twain's attributing Injun Joe's vicious nature to his race. When Joe tells Dr Robinson, "The Injun blood ain't in me for nothing," he is referring to his determination to avenge the minor offenses committed five years previously; the implication is that 'Indians' (Native Americans) do not forgive or forget and that they are ruthless in revenge. However, insofar as Injun Joe's outcast status is concerned, this cannot be taken as a sign of racism on Twain's part, as it is likely to be an accurate reflection of how a half-Indian man would have been treated in a small Southern town at that time.
The Adventures of Tom Sawyer: Novel Summary: Chapter 7 - 9