Fly On the Wall

Removing the part in question would cause the machine to emit a ray that turns a human into a fly. 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.

Episode Summary
While Candace tries to get Stacy's help to figure out what to wear for her surprise date with Jeremy, Phineas and Ferb are trying to figure out what they're going to do after their daily projects parts didn't arrive. Buford and Isabella suggest to modify some of their old inventions, but Baljeet refutes them. Phineas decides to build something new and simple, in the spirit of summer. While the kids all try to remember how they know the song Summer (Where Do We Begin?), Buford inspires Phineas to build a tire swing. Phineas suddenly wonders where Perry went.

Perry enters his lair and is told by Major Monogram that Dr. Doofenshmirtz is "at the shark"; Carl quickly corrects this to "at the park." Monogram sends Perry to deal with the problem, as it is much less heebie-jeebie than he thought.

While the kids are building their giant jet-powered tire swing, Phineas walks away to confirm calculations with Baljeet. Buford fiddles with the controls so as to look busy, and removes a doohickey causing the controls to emit a glowing ray. He quickly replaces the doohickey and asks Phineas what removing that doohickey would do; Phineas figures out it would cause the controls to fire a ray turning a person into a fly, pointing out that removing a different part could turn the controls into a sorbet machine.

Meanwhile, Candace realizes that Stacy's suggestion of a hair bow doesn't look good on her, and goes to remove it, but realizes that she's been turned into a fly. She tries to get Linda's attention, but her mother just shoos her away, thinking she's just a fly. Candace persistently follows Linda and accidentally gets into the car with her, hitting the back windshield as the car pulls away.

At Danville Park, Perry comes across Doofenshmirtz having a picnic. Doofenshmirtz invites Perry to join him, but the cloth gives way and traps Perry in a hole. Doofenshmirtz then reveals his latest -inator: the Feed-the-Pigeons-inator. Perry is unimpressed, but Doofenshmirtz tries to rationalize it by pointing out that feeding the pigeons is prohibited in the park, and is therefore illegal. He then sighs and tells Perry that he's suffering from evil scientist's block, having hit a dry spell during a summer that feels like it's been going on for four years. He asks for Perry's help, and the platypus immediately hops out of the trap and walks away with Doofenshmirtz.

After finishing the tire swing, the kids all test it out. After the initial test with the kids inside the tire, Phineas pushes a button that dangles each of them in individual tires, hanging from the one large tire. Everyone enjoys it. Perry puts Doofenshmirtz through a series of exercises and paintings in order to help him break out of his block, culminating in a successful -inator.

Candace is still trying to get Linda's attention in the car, so Linda rolls down the window, causing Candace to fly out of the car. She then flies throughout Danville, eventually ending up in Jeremy's room. Listening in on his phone conversation with Coltrane, she hears him say that he's taking her to the rodeo. Candace is thrilled because she now knows what to wear, but has to leave after Jeremy tries to swat her. She immediately is forced to flee again, this time from some of the Fireside Girls trying to trap her in a jar, and succeeds, coming across another fly with a human head in the process.

The tire swing ride has ended, and Isabella proclaims it "the most fun ever." They prepare to set up for another ride when Baljeet notices "a fly with orange hair." Phineas looks and realizes that it is Candace, and that Buford had removed the doohickey. Buford messes with the machine again and is able to eventually get Candace back to normal, who threatens to bust them, but thanks them as well. Buford then notices a "FLY" button on the controls and pushes it, causing the tire swing to fly into the air and its supporting pole to end up in outer space. Isabella is disappointed that the fun is over, but Phineas turns the machine into a sorbet maker and offers sorbet to his friends.

Meanwhile, Doofenshmirtz is thrilled that he has created his best -inator ever, and gloats to Perry that since it has no self-destruct feature, there is nothing stopping him from taking over the Tri-State Area. However, before he can finish gloating, the giant tire crushes his -inator. While the kids are eating sorbet, Jeremy arrives in a suit, looking for Candace. She emerges dressed as a cowboy, having planned for the rodeo, but they are instead going to a restaurant pronounced "Ro-DAY-o." Candace laments that it must not be "dress like a cowboy and get your dinner free night," and the waiter confirms: those are Tuesdays.

Songs

 * Summer (Where Do We Begin?)
 * Fly on the Wall

End credits
First verse of Fly on the Wall (during the end credits when broadcast by itself)

The "Too Young" Line
None.

Whatcha doin'?
None.

Perry's entrance to his lair
Perry goes down the basement staircase, stopping at the landing next to the Panic Room, opens the bottom stair, stops himself halfway down the slide after forgetting his hat, retrieves it from the stairs, and goes back down into his lair.

Background Information

 * The kids unintentionally reference the events from "Phineas and Ferb The Movie: Across the 2nd Dimension" when Buford, Baljeet, and Isabella start singing Summer (Where Do We Begin?). Phineas then says "We all know this song...I just don't know how...", confirming that they didn't have their memory of the events of that day back.
 * Doofenshmirtz breaks the fourth wall in this episode, by saying that he feels as if he and Perry had been battling each other for four years, a nod to the fact that this was the first episode produced for Season 4, as well as the length of the series' run.
 * This episode reveals that Bobbi Fabulous wears a wig.
 * It is revealed that Dr. Doofenshmirtz has an uncle named Boris.

Errors

 * In the song, a scene pops up of a calender on June. It folds back a month, but it shows a July calendar. It should have shown May.
 * Also during the song, when Candace enters Bobbi's bathroom, his legs are missing, and only he is inclined, while the bathroom behind him is on the right position.
 * It's unknown how Buford, Baljeet, and Isabella know the song, "Summer (Where Do We Begin?)", because they were not even in the same dimension as Phineas and Ferb when they were singing that song, although this could be explained if Phineas and Ferb had told them about it the same day.

Continuity

 * This is the second episode to feature a character being turned into a fly. In "Picture This", Buford accidentally got mixed with a fly in Phineas and Ferb's machine.
 * Seventh time Candace spends most of the episode after being changed by an invention. ("Does This Duckbill Make Me Look Fat?", "Attack of the 50 Foot Sister", "Split Personality", "Canderemy", "Excaliferb", "Doofapus")
 * Candace is seen as a baby ("Agent Doof"), a praying mantis ("Candace Loses Her Head") and the Giant Floating Baby Head at one point.
 * Second time Isabella sings a part of a song she did not originally sing. The first was Pinhead Pierre Theme in "Magic Carpet Ride".
 * Second time the long run of the show is referenced. Dr. Doofenshmirtz says it feels like the summer's been going on "for, like, four years." ("The Curse of Candace")

Allusions

 * The Fly - Candace gets turned into a fly much like what happens to the main character in the story. The line "Help me" from the 1958 film adaptation is also used.
 * The Son of Man - Doofenshmirtz's painting is inspired by this 1964 self-portrait by René Magritte, depicting the artist with an apple obscuring his head.