When Phineas, Ferb, and Perry follow Dr. Doofenshmirtz through his "Otherdimensionator", they find themselves in an alternate universe where a second, truly evil Dr. Doof rules over his Tri-State Area with an army of iron-fisted robots. To save his friends from certain doom, Perry makes the ultimate sacrifice by revealing his secret identity as Agent P. Phineas and Ferb escape, meet their 2nd dimension selves, and begin their own mission to rescue Perry.