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?

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.

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

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?

The kids in Room 3B are holding a Sharing and Caring Tag Sale to earn money for charity. Song Lee and Ida are selling friendship bracelets, Doug is selling books, and Sid is selling delicious, fresh-baked chocolate chip cookies. But something else is on Harry's mind: his grandmother is having money trouble, and Harry wants to help. So he comes up with a plan to raise money for her. The problem is that Harry doesn't realize his plan involves stealing from the class's charity collection! How can Doug stop his friend from becoming a horrible thief? Could the answer come from one of Sid's delicious cookies?

Every Halloween Harry plays tricks on his classmates and dresses up as something scary or gross or both. He's been Count Dracula, a slimy snake and even the Loch Ness Monster. Everyone in Room 3B is waiting to see what Harry will be this year--and they're all in for a really big surprise! "There's laughs aplenty in the short snappy text--just the thing to turn new readers on to books."--Booklist for Horrible Harry and the Green Slime