While on a mission to prove to Merlin that they can use magic wisely, Jack and Annie travel to seventeenth-century Venice, Italy, to save the city from disaster.
Fifth-grader Winnie, with notes from her friends, writes of turning her treehouse into an embassy after her newly-divorced parents become unreasonable, where she is joined by nine others with complaints.
Their magic tree house takes Jack and Annie back to retrieve a lost story in ancient Greece, where they witness the original Olympic games and are surprised to find what girls of the time were not allowed to do.
Jack and Annie are whisked back in time to Old Philadelphia by the magic tree house to meet the Founding Father, journalist, and famous inventor Benjamin Franklin.