User blog comment:Mobo85/Hot off the Presses: "Across the Second Dimension" Debuts August 5/@comment-406459-20110620201728/@comment-970465-20110621023008

J.Severe: I think the sequence of events goes:

-Phineas and Ferb wake up and Everything's Better With Perry happens -Perry gets sent on his mission -Phineas and Ferb play giant badminton and accidentally crash into DEI. -Perry goes into pet mode on seeing them. -They go to the second dimension. -Doofenshmirtz stays and Phineas and Ferb go to meet their alternate selves. -Phineas and Ferb return and alternate Doofenshmirtz tries to kill them, so Perry saves them, but gets stuck in the skull and captured. -Phineas and Ferb end up with the resistance. -They bring original Candace over for some reason. -The resistance invades evil Doofenshmirtz's headquarters. -Phineas, Ferb and Candace are captured. -Doofenshmirtz was also captured at some point, and alternate Doofenshmirtz tries to feed the five characters to a goozim. -They escape and travel through a bunch of different dimensions. -They get back to their dimension, which alternate Doofenshmirtz is invading.

And then I guess there's some sort of battle. Also, at some point alternate Perry switches sides.