Each day, two kindhearted suburban stepbrothers on summer vacation embark on some grand new project, which annoys their controlling sister, Candace, who tries to bust them. Meanwhile, their pet platypus plots against evil Dr. Doofenshmirtz.
National Hockey League star Luc Robitaille offers his assistance when Phineas and Ferb take an ice hockey game to the extreme. Meanwhile, Doofenshmirtz build an Abominable-inator to make himself bigger, scarier and hairer.
Phineas and Ferb plan their own New Year's Eve ball drop, complete with a customized multi-dimensional ball, while Candace makes it her resolution to refrain from busting her brothers before the clock hits midnight. Meanwhile, Doofenshmirtz uses a Resolution-Changer-inator in his tie as he continues the never-ending attempts to take over the Tri-State Area.
Buford removes a part from a tire swing the boys are building and it accidentally shoots a ray that turns Candace into a fly. Meanwhile, Doofenshmirtz is suffering from evil scientist’s block.
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.
It's time for Danville's Doo Wop Hop and car show and the whole town is getting prepped for it. Doofenshmirtz is set on winning the show even if it means using his Rust-inator to turn all the other cars into red dust. Meanwhile, Candace's hope for a car of her own has come true, but it's not quite all she imagined.
The boys create Rutabaga-themed vehicles when Candace is chosen to be Rutabaga princess and gets to start the "Running of the Chinchillas." Across town, Doofenshmirtz plans to turn himself into a real live Kinderlumper to scare Roger into relinquishing control of the Tri-State Area over to him.
Agent P teams up with an estranged former human partner named Lyla to stop a hijacked train to save the train's passengers and Canada's national treasure - a moose named Albert.
Perry comes face to face with an Australian platypus hunter set on destroying him. Baljeet is having an existential emergency and finds himself incapable of making decisions.
The gang switches bodies with alien tourists for a free intergalactic vacation.
The boys create a new invention using recycled parts from past projects. When Candace attempts to bust them, Mom is too exhausted from baking pies all night and can't figure out what Candace is trying to show her.
The boys make a giant inflatable wading pool for Mom. Candace reveals her "Emo" side. Doofenshmirtz attempts to become ruler of all bees.
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.
When Candace thinks Jeremy is bored with their usual hangouts, she sets out to find something unique to do with him. Meanwhile, Phineas and Ferb power through town surfing on a giant ball of water and Doofenshmirtz plans to use his Double-Negative-Inator to confuse his local eatery into giving him a wintery drink that is usually not served during summer.
When Pinky goes missing, Phineas & Ferb create a machine that will amplify Buford’s senses to those of a dog’s. However, it works so well that the animal agents’ secret identities are put in jeopardy. Meanwhile, Candace tries to meet up with Jeremy for lunch at City Hall but gets stuck in a mandatory tour.
Dr. Doofenshmirtz and Major Monogram have their hearts set on revealing the top 10 musical numbers from Seasons 2 and 3, but soon find out that celebrity host Kelly Osbourne has been brought in to fill the role. Unwilling to submit to playing second fiddle, Doofenshmirtz makes it his mission to thwart Kelly until Perry the Platypus sets out to stop his nemesis from ruining the entire show. Maia Mitchell ("Teen Beach Movie") also guest stars.
Candace thinks she can trap the boys at last when they ask her to call Mom if they get stuck in their giant Gordian Knot, but is distracted by helping Jeremy open his mini-safe.
Phineas and Ferb build a wall for climbing. Candace is recording a Fireside Girls book with Irving and loses her voice. Meanwhile, Dr. Doofenshmirtz creates the Just-Desserts-inator.
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.
Phineas and the gang celebrate Isabella's birthday in a big way, but all she really wants is some quiet time with Phineas. Meanwhile, Doofenshmirtz has installed his Bugs Me-Inator onto an evil bug bus and is driving around Danville turning all the things that bug him literally into bugs.
When Linda becomes overwhelmed for organizing a block party, she asks Phineas and Ferb for help. Norm falls in love with Rodney's female robot.
Candace and Stacy compete in Phineas and Ferb’s Ultimate Obstacle Course. Doofenshmirtz plans to humiliate his brother, the Mayor.
Spider-Man, Iron Man, Thor and Hulk stand powerless after being struck by Dr. Doofenshmirtz's power-draining "inator." Once the supervillains – Red Skull, Whiplash, Venom and M.O.D.O.K. – find out that Dr. Doofenshmirtz is responsible for robbing the superheroes of their powers, they seek him out and together create mayhem in Danville. Meanwhile, Phineas and Ferb do everything they can to restore the superheroes' powers before the evil villains take over the world.
After learning about Monty and Vanessa's secret relationship, Carl bribes Monty into helping him get some much needed acknowledgement from Monogram. Meanwhile, Candace is ecstatic when she discovers that her neighbor Peggy McGee has witnessed all of Phineas and Ferb's summer antics and is happy to tell Mom about them. Also, Dr. Doofenshmirtz creates its "Inflator-inator" to try to silence his neighbor who plays the bagpipes every day.
Inspired by Candace's book club selection, The Iliad, the boys reenact the Trojan War -- but with a Phineas and Ferb twist. Meanwhile, Perry discovers that Doofenshmirtz has a major problem with throwing things away so he helps him find his De-Clutter-Inator.
Phineas and Ferb deejay at Vanessa's Halloween party. Doofenshmirtz hunts for hidden treasure in a castle.
Candace brings her plush Ducky to life. Doofenshmirtz encounters a Giant Floating Baby Head. Phineas, Ferb, and their friends confront a horde of evil platypuses.
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 Candace is stumped about what to get Jeremy for his birthday, she reluctantly asks Phineas and Ferb for their help in creating the ultimate gift. Meanwhile, Doofenshmirtz plans to make fears a reality with his Worst-Fear-Inator, but his plans backfire when he finds himself battling his own fears instead.
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.
When Candace is accidentally zapped by Doofenshmirtz’s Stinkelkrampen-Inator (aka Good Luck-Inator), she realizes she has a good chance of busting Phineas and Ferb.
Annoyed at waiting in really long lines at the return counter, Doofenshmirtz invents a "Back-to-the-Store-inator" to send things back to the store where they came. Meanwhile, Phineas and Ferb stage an extreme batting challenge their friends take place in, and Candace's obsession to bust coincides with her and Jeremy's visit to the Extreme Water Park.
Agent P travels to the glamorous city of Montevillebad to stop Doof from winning the Grand Prix and collecting the prize money. When Doof uses his "I-don't-care-Inator" to sabotage the race and eliminate the competition, including international racing legend of Italian-Scottish-Swiss-Dutch descent Paolo Vanderbeek (Patrick Dempsey), Agent P must take the wheel and go head-to-head with Doof on the racetrack.
Doof's latest inator changes the way the Earth moves and it is up to Phineas and the gang to save summer.
Perry helps Doof in retrieving his father's old lawn gnome. Meanwhile, Phineas and Ferb help out their father on Father's Day
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.
Doof gets rogue OWCA agent Dennis the Bunny to escape prison. Meanwhile, Phineas and Ferb make some improvements on the Fireside Girls' marionette show.
Buford and Baljeet get in a food fight while Ferb is at the dentist. The Fireside Girls help Isabella plan a romantic picnic with Phineas. Meanwhile, Vanessa wants to go to a movie marathon, so Doofenshmirtz creates a Teleport-inator.
Phineas and the gang help Love Händel prove the existence of Klimpaloon, the magical old-timey bathing suit that lives in the Himalayas, to verify that their song, "The Ballad of Klimpaloon", is legitimate.
Isabella unintentionally admits her feelings for Phineas in a letter. Meanwhile, Doof invents an inator to help change his misfortune
Candace is accidentally hit by the Impersonator-inator which changes her appearance to a pizza delivery guy, but uses this appearance to help her better understand boys.
In a parallel universe far, far away, Phineas and Ferb are tasked with returning the Death Star plans to the Rebel Alliance before Storm trooper Candace catches up to them. Meanwhile, complications arise when Perry is trapped in carbonite.
Doofenshmirtz gets kidnapped by Professor Mystery. Phineas and Ferb find a capsule with Bernie and Denise.
Doofenshmirtz teaches an Inator Method seminar.
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.
After Doofenshmirtz is defeated, a new threat in the 2nd Dimension emerges, leaving it up to Phineas, Ferb, Candace and her resistance fighters to defeat this new foe.
After facing the choice of imprisonment or community service, Doof becomes a teacher at Vanessa's school. Meanwhile, a trio of bugs embark on a journey to become the first insects to communicate with humans.
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?
Duplicate (DELETE), was a duplicate of Season 2's "The Secret of Success".