After Jack and Annie find a magic treehouse in the woods near their house, they can't believe it when they are transported back to the time of the dinosaurs. The siblings return to the treehouse to prove their adventure really happened and find themselves traveling back in time to the Middle Ages. They meet a mysterious knight who needs their help but while they are searching for him in the castle, the kids are mistaken for spies and thrown in the dungeon. There, they befriend the other prisoners who seem to be imprisoned for trivial crimes, so Jack and Annie come up with a plan to escape and free the prisoners.
