Working on a dragon project in Room 3B leads to a war between two good friends--Harry and Song Lee.

Horrible Harry falls in love with Song Lee, and Harry's best friend, Doug, can't stand all that mush.

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.

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.

As the last day of third grade looms, Doug learns that Harry is moving to a new town and wonders how he'll survive fourth grade without him, while Harry wonders about the new neighbors across the street and what they could mean for their friendship.