Working on a dragon project in Room 3B leads to a war between two good friends--Harry and Song Lee.

The students in Miss Mackle's third-grade class enjoy a day of Halloween surprises, including Harry's unusual costume.

Harry and his detective classmates try to find clues relating to a mysterious locked closet in Room 3B.

When Horrible Harry's pet cat, Googer, sneaks a ride and gets into the school building, third-graders Harry and Doug have to catch him before anyone else does, which means going into some forbidden places.

As Valentine's Day approaches, the students in Room 2B are preoccupied with kickball and a possible wedding between Horrible Harry and Song Lee.

Song Lee is upset when she receives hateful notes in class, but she finds an appropriate and positive way to deal with them.

On the last day of second grade, Song Lee's party at the local amusement park forces Harry to face his fear of elevators when he is expected to ride the Drop of Doom.

Spurred on by the promise of a mystery prize, Harry and Doug are determined to win the most points on Field Day, but Harry's sneaky tactics annoy their competition, making the two boys targets for revenge.

It's almost summer vacation and the students in room 2B are having trouble concentrating on their butterfly project, until a frightening-looking new teacher comes to supervise the Suspension Room and Harry is sent there as punishment for unruly behavior.

Inspired by his third-grade class's study of the moon, Harry announces that he is going there.