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

Horrible Harry falls in love with Song Lee, and Harry's best friend, Doug, can't stand all that mush.

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

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

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.

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

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.

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.

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...

Miss Mackle's third graders share December holiday traditions--Christmas, Hanukkah, Kwanzaa, Three Kings Day, and Korean New Year--with each other and with Harry's great grandfather, who has just moved to a nursing home.