Phineas and Ferb are playing soccer in their back yard when Heinz Doofenshmirtz (2nd Dimension) comes by from the Other-Dimension-Inator. Phineas says "What in the.....?" Moments after, Candace Flynn (2nd Dimension) comes by and Phineas says "Whoa! Check out Candace's outfit!" Candace then says that she needs Phineas and Ferb's help. Phineas questions why is Candace 2 dressed the way she is. Candace 2 says that she is from another dimension. Phineas stutters and says "Riiiiight.....", but Candace 2 says there is no time to explain. She says that Heinz Doofenshmirtz 2 is trying to take over Phineas and Ferb 1's dimension, and they have to stop him. Phineas then wonders where Perry the Platypus went off to. Perry is by Heinz Doofenshmirtz and Heinz Doofenshmirtz 2. Heinz Doofenshmirtz 2 says that with his army of Norm Bots, that he will take over the world. Heinz Doofenshmirtz 1 then moves a switch so the Norm Bots can go terrorize the Tri-State Area. At this time, Agent P leaves. The people when they see them start to scream. Candace 2 tells everyone that Agent P had confirmed that Heinz Doofenshmirtz and Heinz Doofenshmirtz have unleashed an army of Norm Bots to destroy the city. Phineas thinks that is cool that Perry is a secret agent. Candace tells that he has all of their inventions in storage. Phineas then says it is time to take down the Norm Bots.
You send units to battle to destroy the Norm Bots by collecting gears. If you get hit, the defender's health goes down. If it goes down to nothing it will either explode(items) or leave the area(animals/humans). Try to keep the Norm Bot count low that get away from you, otherwise the level ends. On the bottom of the screen, it shows where the next wave of Norm Bots are, which you can skip to the next wave if you want. There is also a survival level, where you are going against the Norm Bots and Perry the Platyborg for 10 minutes.
The player starts in levels 1-4 with 100 gears, and in levels 5-10, the player starts with 75 gears.
This game is similar in game play to a Tower Defense game, which also requires you to strategically place your defenses to slow down and eliminate enemy units before too many get past you.
A reskinned game, The Walking Doof premiered October 2, 2014. All the Fireside Girls return from the first game (except for Adyson and Isabella [ even though she is on the title screen]), also Candace, Vanessa, Baljeet, and Buford are buyable, making it the first game Vanessa can be used in anyPhineas and Ferb game.