When Sid, his annoying third-grade classmate, ruins Song Lee's origami praying mantis, Horrible Harry plots triple revenge on the troublemaker.

Ruby and Mia are total opposites. Ruby is a little awkward, not a "joiner," and loves to write poetry. While Mia is type A, popular(ish), and wants to be class prez. They used to be friends. But now they have nothing in common anymore...or do they?

Doug discovers that though being Harry's best friend in Miss Mackle's second grade class isn't always easy, as Harry likes to do horrible things, it is often a lot of fun.

"Doug is infested with the one creepy-crawly thing Harry hates: lice! Will Harry be able to help Doug get rid of them, or will Doug have to pack up and move to a new country instead?"--

Horrible Harry, the class clown of Room 2B, returns to the spotlight with the Purple People, mysterious beings that only he can see.

Harry persuades his classmates to sneak through the playground fence during lunchtime recess to view some unusual mushrooms.

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.

When the origami pig that Song Lee made for her grandmother is seized by a substitute teacher, the usually well-behaved third-grader breaks a classroom rule to rescue it from the "June box."

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.

Dorothy's aunt and uncle get acquainted with Oz after they lose their farm and Ozma invites them to live with her.