Needing to find a tool that can fuse metal with wood, Phineas and Ferb go to the future on a time machine, and also encounter the future children of the Flynn-Fletcher family. Meanwhile, reminded of their past, the future Candace decides to go back in time and successfully bust Phineas and Ferb's rollercoaster project, but her actions cause a chain reaction which turns the future into a dystopian society led by Dr. Doofenshmirtz. As a result, Future Candace enlists the help of her present brothers to help fix her future.