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.

"It's Mary's birthday party. When things go horribly wrong will Harry be able to save the day?"--

"Best friends Harry and Doug must find their teacher's missing diamond in time for the class talent show."--

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

Spurred on by the promise of a mystery prize, Harry and Doug are determined to win the most points on Field Day, but Harry's sneaky tactics annoy their competition, making the two boys targets for revenge.

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

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

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.

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.