When his friend Doug is infested with head lice and Mary convinces everyone to stay away, Harry and his other friend Song Lee stand by Doug and declare war on the bugs.

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.

Third-grader Harry thinks of a way to patch up a conflict with his schoolmate Mary and include his friends in a fun detective case with rewards for everyone, including Grandpa.

"Horrible Harry says goodbye in the 30th anniversary finale of a beloved series! The last day of third grade is approaching fast, but a farewell to Room 3B isnt the only goodbye Doug has to say this year. Song Lee and Mary are busy preparing an end-of-year present for their favorite teacher, Mrs. Flaubert, but their excitement cant distract Doug from Harrys suspicious silence. When Harry finally admits that his family is moving to a whole other town,...