When Phineas and Ferb find out that their grandma Betty Jo used to be a roller-derby queen, they build an awesome rink—right in their backyard! Soon they discover that Jeremy Johnson's grandmother used to be their Grandma's skating rival, so they set up a contest to see which granny can roller derby her way to the finish line the fastest. The thrills continue when Phineas and Ferb build a gorge so their grandpa can do a radical stunt jump over it!