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?

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.

After four days in a row of indoor recess, Miss Mackle's students are bored-until Harry decides to solve the biggest mystery ever in Room 3B! There's a locked closet in the classroom that's been sealed off for years, and he wants to know what's inside. So Harry drafts Doug, Song Lee, and the rest of the class to help him investigate. Their search reveals many surprises-from a hidden trapdoor to...eyeballs! What secret treasures does the closet hold? Is it something more horrible than even Harry can imagine?

Harry's in love, and his best friend, Doug, is disgusted -- Harry won't even throw snowballs at girls anymore. Will Harry ever go back to being his horrible self?"Kline captures perfectly the crowd scenes and private moments in the classroom."-- Booklist

With Valentine's Day right around the corner, Harry hatches one of his bright ideas. He's going to stage a wedding—to Song Lee!

Horrible Harry has caused a lot of trouble at school before, but he's never caused trouble like this. When Sid ruins an origami animal Song Lee made, Harry defends her by declaring triple revenge! No one knows when, where, or how, but Harry is going to get Sid back. Will it be on pajama day, when the kids wear their nightclothes to school? Will it happen in Room 3B? Or will Harry's ultimate revenge mean Sid is the only one not invited to Harry's ninth birthday party?