The Magic Tree House adventures continue in books 9-12. Morgan the magical librarian of Camelot challenges Jack and Annie to discover the answers to four riddles as they travel under the sea to the Wild West, the African plains, and the frozen Arctic. If they succeed, they will become Master Librarians!

Books in this set include: Dolphins At Daybreak (9), Ghost Town At Sundown (10), Lions At Lunchtime (11), Polar Bears Past Bedtime (12).