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.
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.
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.
The students in Miss Mickle's third-grade class enjoy a boat trip on the Connecticut River after a class discussion of ancestors reveals that Sidney and Ida both have connections to the sea.
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.
On the last day of second grade, Song Lee's party at the local amusement park forces Harry to face his fear of elevators when he is expected to ride the Drop of Doom.
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.
Horrible Harry tries to use the Fibonacci sequence to solve cafeteria worker Mrs. Funderburke's secret code and secure his position as the best detective in the school.
Originally published: New York : Viking, 1995. Harry plots revenge against Sidney, the class tattletale, when Miss Mackle's second graders go on a field trip to the pond. "Early Chapter Books" collection--look for orange spine label.