Harry leads a mission to place cobwebs all over school, shows the class how to make green slime, and stages a "deadly skit" that has everyone on the edge of their seats.

Follows the school activities of second-graders, Harry and Doug, as they participate in a secret mission to celebrate "Charlotte's Web," learn how to make green slime, and put on a skit warning about the dangers of smoking.

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.

The holiday season is here, and the kids in Room 3B are learning about all the different ways people celebrate. In addition to Christmas and Hanukkah, there's Kwanzaa, Three Kings Day, Korean New Year, and more. All the talk about holidays has everyone feeling festive. Everyone, that is, except Harry. He doesn't seem to care about the holidays, the class pet, or even the new student in class. It's clear that something is bugging Harry—but what could it be?

Another fun mystery starring Horrible Harry, and this time he's calling the shots! Harry has always loved solving mysteries, and now his friends in Room 3B have learned to love it, too. So Harry challenges them to figure out what he has hidden in his giant, old suitcase. Led by a very determined Mary, the kids take turns solving clues and piecing the mystery together. Their hunt leads them from the classroom to the library, and even to Harry's grandfather's nursing home. Will they be able to solve Harry's mystery? Or will things go horribly wrong for the novice detectives?

It?s a busy time in Room 2B?an ant observation project is beginning, Miss Mackle is teaching square dancing, and class pictures are being taken. Then one of the fish from the 2B fish tank goes belly-up! Is Harry to blame?

Room 2B been invaded by purple people! That's what Harry is saying, but no one else believes him. Can he prove that the purple people are real?