Henry's parents find a statue of King Ioda of the Lost City of the Littles. Dr. Hunter wants a look at the statue's inscription, and so do the Littles.
In wanting to join an exclusive boys club, the Fire Wheels, Henry almost gets hurt trying to perform a dangerous stunt, a task that was requested by Mike, the club leader.
When it gets too risky for the Littles to continue watching movies in the Bigs' theater, they decide to make their own movie using Henry's home movie camera.
During a very rainy night Grandpa Little is telling the story of Dr. Frankenlittle's monster when suddenly swarms of huge black rats invade the Little's home!
It is report card day and one of Henry's classmates, Marie, is told by her father that unless she gets straight A's, he will send her off to private school, away from her friends.