Tom, cheered up by Aunt Polly's forgiveness, runs over to Becky Thatcher and apologizes for acting like a jerk.
Unfortunately, Becky does not return the favor, and tells him to get lost.
Tom is so flabbergasted he can't come up with a retort, not even a bad one. He walks into school feeling absolutely terrible.
Now, as it turns out, old Mr. Dobbins, the schoolmaster, is a creepy, sad guy. He once dreamed of being a doctor but, having failed to achieve his goal, has settled for something rather less glamorous: he keeps an anatomy textbook in his desk drawer, and glances at it during class whenever he can.
Becky, curious girl that she is, sees the drawer unlocked, and decides to take a peek at the mysterious book. She opens it up, at random, to a picture of a naked man.
Just then, Tom Sawyer appears behind her, causing her to slam the book closed in fright – and tear a page in the process.
Becky, realizing that she's in for quite a beating, shoves the book back in the drawer, bursts out crying and starts blaming Tom almost simultaneously. She's scared that Tom will rat on her and get her whipped for the first time in her life.
Tom, an old pro when it comes to getting beaten, knows that the schoolmaster will figure things out right quick and, after a bit of thinking, rejoins his fellows in the schoolyard.
When class starts back up, Tom's spelling book is quickly found to be a mess. Becky decides not to speak up, and he takes his punishment like a man.
When the lessons are finished, and the students have begun to study, Mr. Dobbins sits back and takes out his special book. Tom considers running up and grabbing it out of the schoolmaster's hands, but by then it's too late – he has noticed the tear.
Enraged, Dobbins goes down the line, asking each student in turn if they tore the book. When he gets to Becky, she clams up, stutters, and generally looks as guilty as one could possibly look.
Just then, when her punishment seems unavoidable, Tom stands up and takes the hit. He lies and tells Dobbins he's the culprit.
Dobbins, who's a bit of a sadist, gives Tom a heck of a whipping, and forces him to stay at school for two extra hours, but he doesn't care; his sacrifice wins back Becky.