Tarzan and the Knights of Nimmr

Upon finding a crashed balloon, Tarzan searches for its pilot which leads him to the Valley of Nimmr where he encounters knights that end up taking him to Queen Grenalda. He soon encounters the balloonist Annie Talbot who is a writer. When the queen falls ill and Sir Mallad has Tarzan imprisoned in the dungeon, Tarzan learns from the Queen's Royal Physician Sir Ronald that Sir Mallad plans to steal the throne from Queen Grenalda.