This is the last mission for Jack and Annie as Master Librarians. The Magic Tree House takes them to ancient Greece where the Olympic Games are taking place. With the help of the famous philosopher Plato, they get the book they need to save. He also invites Jack to watch the Olympics. However, females in ancient Greece are of low status. They are not allowed to attend the games. Being a smart and brave girl, Annie disguises herself with a helmet and sneaks into the crowd. However, she gets too excited and her helmet falls off!

The guards at the Olympic Games are now chasing after them. Can they escape and go back home? Will they be stuck in Greece on their last mission?