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.

Horrible Harry of classroom 2B cuts back on his mischievous pranks after falling for Song Lee.

When their teacher ends up in the hospital, the members of class 2B find a way to include her in their holiday celebration.

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.

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.

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

Room 3B just learned that Ida had an ancestor who sailed on the Titanic and lived to tell about it! Miss Mackle decides that she will take the class on a real riverboat trip. But has something gone wrong.

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

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

Horrible Harry sets out to discover who Miss Mackle is going to marry, and he takes some risky moves to be the first one to know.

Horrible Harry must defend his reputation as a detective by cracking the secret code of Mrs. Funderburke's lunch prizes.

Harry and Doug investigate when special bookmarks begin to disappear while their class is busy studying poetry and running their own post office.

While Harry's third-grade class is studying birds, the cold winter weather keeps them cooped up inside during recess and Harry gets restless.

Everyone in Room 3B knows that if Miss Mackle sees you playing with toys at your desk, she'll confiscate them for her June Box. So when a substitute teacher catches good girl Song Lee with a pink origami pig, into the June Box it goes. The problem is that this origami was to be a birthday present for Song Lee's grandmother. So Song Lee does the unthinkable: she breaks into the June Box to free her pig. Now Harry, Doug, and the rest of the kids have...

"Harry considers stealing from Room 3B's Sharing and Caring Tag Sale in order to help out with money problems at home"--

Nearly every kid in Room 3B is trying to get picked for the South School Safety Patrol Squad--especially Harry. Harry wants a star badge just like his grandpa's, so he works extra hard to be the perfect student: hanging up his jacket neatly, organizing the crayons in rainbow order, and--his favorite part--cleaning up sticky noodles off the floor after lunch. But Doug thinks someone is taking the power of Safety Patrol too far, maybe even using it...

When his best friend Doug discovers his top-secret hideout, Harry enlists his friends' help to save it from being developed into an apartment building.

"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?"--

As the last day of third grade looms, Doug learns that Harry is moving to a new town and wonders how he'll survive fourth grade without him, while Harry wonders about the new neighbors across the street and what they could mean for their friendship.