Reading Level: grade 3. Interest Level: ages 8-10. The ninth book in the Captain Underpants series doesn’t actually feature very much of Captain Underpants or Tippy Tinkletrousers, though his return brings about catastrophic results. What it does provide is the back story of how George and Harold first met and their run-ins with the school bully, Kipper Krupp. Rest assured there’s plenty of action, pranks, laffs, and heart too. (Captain Underpants series)