Phineas and Ferb create a life sized maze filled with fun obstacles. Melissa, the leader of the Little Sparks, a younger branch of the Fireside Girls, is immediately captivated when she meets Candace and finds out that she was a Fireside Girl who earned 50 patches in one day. When the girls try out the maze, Candace takes charge, but things don’t go as planned. Meanwhile, Dr. Doofenshmirtz reasons that if the Leaning Tower of Pisa can generate souvenir revenue, then surely he can use his latest invention, the "Tilt-inator," to tilt buildings so he can sell souvenir replicas.

Phineas and Ferb plan to put Danville on the map by building the world's tallest building. However, Candace teams up with Albert and utilizes his expertise to bust her brothers. Meanwhile, Dr. Doofenshmirtz wants to be responsible for all the evil in the Tri-State Area, and since he believes that evil levels rise during a full moon, he plans to rotate it so that only the infamous "dark side of the moon" faces Earth.

Candace switches places with a princess who looks exactly like her, while the real princess helps the boys build a giant jukebox filled with live bands.

The third season begins with Phineas and Ferb building a gigantic biome during a bit of bad weather to help Isabella earn a Fireside Girl patch.

It's Phineas' birthday and for the special occasion, Ferb puts together a clip show of the gang's favorite moments. Meanwhile, Agent P has to stop Dr. Doofenshmirtz from using his 'non-inator' to pre-empt his brother's biography from appearing on television.

When Candace discovers that Phineas and Ferb have invented a computer that can answer anything, she asks it how she can finally bust her brothers once and for all. Meanwhile, Dr. Doofenshmirtz loses the key to his latest invention, the "All Purpose-inator," and Agent P must find it before he does.

Mom joins Jamie Oliver as one of the judges for Danville's Meatloaf Festival Cook-off, as he stresses healthy eating and fresh ingredients. Meanwhile, Candace puts a bid on a prized souvenir resembling band members Nigel and Adrian from her favorite band, Tiny Cowboy, at the Rock and Roll Memorabilia Auction, but gets distracted when her brothers build a bounce house in their backyard. On the other side of town, Dr. Doofenshmirtz has plans to enter his family meatloaf recipe into the competition using "hate" as the special ingredient.

Phineas and Ferb enlist the help of cyclist Greg LeMond to help Baljeet compete in a bicycle race. Meanwhile, Doofenshmirtz tries to bring the city to a standstill so he can bid on an auction unopposed.

It's Halloween night and the kids encounter a strange boy named Russell who is convinced his house is haunted. Meanwhile, Dr. Doofenshmirtz's disdain for grass causes him to invent a "mind-transfer-inator" enabling him to merge minds with a cow and destroy all the grass in the Tri-State Area. Unfortunately, his plan backfires and he transforms into a scary "were-cow" that wreaks havoc any time there is a full moon. It's now up to Agent P to stop him and save Danville.

When Phineas and Ferb are inspired by an antique escape chamber that Dad acquires, they decide to build a computer-controlled tower that will trap them inside and allow them to explore the world of escapement. Meanwhile, Dr. Doofenshmirtz invents a "Rude-Inator" to ruin Roger's meeting with a visiting dignitary from England.

After locating and retrieving the Amulet of Juatchdoon, adventuring archeologist duo Ohio (Phineas) Flynn and Rhode Island (Ferb) Fletcher set off to South America to help Damsel in Distress Isabella find the Lost Temple of Juatchadoon and her missing mother. However, Dr. Doofenshmirtz has other plans for the amulet - to awaken the evil corn colossus to give him the power to destroy the world.

When Mom is out of Doonkleberries for her famous Doonkleberry pie, the boys set out to find some for her. Meanwhile, Perry and Dr. Doofenshmirtz find themselves across the ocean as Doofenshmirtz returns home to renew his Druesselsteinian driver’s license. Back in Danville, Candace is convinced she has discovered the answer to her busting problem.

When Baljeet becomes concerned that he is losing his mental edge, the boys invent a cerebral stimulatory hat, or "Brain booster," to help him. But when the hat exceeds expectations and makes Baljeet exponentially smarter, he suddenly views everyone else as beneath him and becomes a threat to civilization by taking Earth's atmosphere and bringing it to the moon. Meanwhile, Dr. Doofenshmirtz plans to use his "Key-Find-Inator" to collect all the keys in Danville in hopes that it will lead to the Key to the City.

Candace finds it difficult to bust Phineas and Ferb when her brothers build nanobots that can assemble into any object they can imagine. Meanwhile, Dr. Doofenshmirtz has jury duty, so Norm takes over the day’s evil scheme -- to destroy Danville by using weapons.

The Flynn-Fletchers are off on an African safari, leaving Perry at home to deal with Doofenshmirtz and his most evil plot yet: to take over the O.W.C.A. But when Doofenshmirtz accidentally zaps Carl the intern with his Ultimate-Evil-Inator ray, Carl takes over the O.W.C.A. (Organization Without a Cool Acronym) and imprisons Doof and Monogram. Agent P steps in but gets zapped with Doof’s many rays and in the cliffhanger of all cliffhangers, disappears.

Candace challenges Buford to keep Phineas and Ferb’s invention from disappearing so that she can sweep in and casually bust her brothers. Across town, Doofenshmirtz has had one too many lattes and is experiencing an extra burst of evil energy.

Isabella and the Fireside Girls turn themselves into bees. Poofenplotz tries to become Queen of the World by stealing and consuming massive amounts of royal jelly.

The boys set out to prove the existence of the elusive Chupacabra to the world, but Candace can't stand the wait and needs to first just prove it to Mom. Meanwhile, Doofenshmirtz has the brilliant idea to use his Switch-Place-Inator to remove hair from one person and give it to another so that he can in turn sell his hair growing tonic.

The gang switches bodies with alien tourists for a free intergalactic vacation.

After studying hours of horror movies, Doofenshmirtz develops a theory that enlarging small, cute animals into giant beasts will help him take over the Tri-State area. But when he puts his plan into action, he soon realizes it might be too much for him to handle. Meanwhile, Phineas and Ferb make a giant revolving foam city so they can safely perform skateboarding tricks, and Candace's tour of the Danville Space Laboratory gives her an opportunity for a high-tech bust.

When Phineas and Ferb discover a commemorative coin from the 1903 Danville World’s Fair, Lawrence recounts the events of the festival to them, in which steam-driven devices were introduced and a set of kids, who were very much like them, were preparing for the highly anticipated event.

Phineas and Ferb have created a device reinforcing the wind and test them on a giant kites in the park. Candace thinks she's finally going to bust when Mom gives her backyard a makeover. Meanwhile, Doofenshmirtz builds a Water-Zalewator to celebrate his girlfriend of the past, who doused him with water, because Heinz she loved, but who then gave him the basket.

Doofenshmirtz's latest "inactor" turns Danville citizens into contagious zombies. Agent P. and the gang try to save the town and avoid becoming zombies themselves.

It's been 10 years after the events of the present, and Phineas must decide what university to go to. After discovering that Isabella had a crush on him for years, Phineas must reach her before she leaves for college and express his true feelings for her. Meanwhile, Doofenshmirtz has a mid-life crisis.

It's the last day of summer vacation and Phineas and Ferb decide to seize the day and make the most of it. Unfortunately for Candace this means it's also her last chance to bust her brothers... or is it?