Phineas and Ferb's Quantum Boogaloo

Phineas and Ferb travel to the future to find a tool that fuses metal with wood. There they encounter a 35-year old Candace who follows them back through time and finally busts her brothers as they are building their rollercoaster, but also accidentally foils Agent P's defeat of Dr. Doofenshmirtz, setting off a chain reaction that turns the future into a dystopian society.

Episode Summary
Phineas and Ferb are in the backyard with Baljeet, making a "superstructure." Phineas says they need a tool that fuses metal and wood, which will only be available 20 years into the future. Baljeet reveals his formula for time travel, which is not yet perfected. Phineas suggests they use the museum time machine from It's About Time! Bailjeet leaves angrily saying “Thanks for inviting. . . me!”—he wasn’t in that episode. The boys and Isabella, who has just arrived with her usual query, leave for the museum, with a somewhat insane Candace following them. There, they depart for the future, with Candace staying behind to bust them when they return, right at that spot (or perhaps a little to the left). In the future, Phineas leaves Isabella with the time machine, claiming she's "the only one they can trust." However, about a minute later, Isabella, in a fit of lovestruck absentmindedness, leans against the machine’s lever, and departs for the past. Phineas surveys the changes made to Danville before spying a older, calmer Candace, along with her children Amanda, Xavier and Fred in the backyard. Amanda complains about how Xavier and Fred are wasting their summer vacation, then complains to Candace that the boys never do anything. Phineas and Ferb talk to their future nephews, and are disappointed by their lack of imagination of what to do with their vacation and offer suggestions with a song by Bowling for Soup. Xavier and Fred decide to build bumper cars that travel in the 5th dimension, and give Phineas a wood-metal fuser. Candace spies the young Phineas and Ferb through the window (as usual) while talking to still-friend Stacy (who has become the president of Uruguay), and goes to spy on them. Once she gets spotted, she runs to get future Linda (still “Mom”) in order to finally bust the boys.

Isabella returns to the future at the museum, displaying various time-travel souvenirs, as the boys climb in. Old Candace drags Mom through the future museum just in time, but Linda gets distracted by an old dinosaur bone and misses the time machine disappearing. Back in the present, a parallel scene unfolds with present Candace and Linda: Mom misses the arrival, remarking on the size of the dinosaur whose bone was unearthed, which is the one the future Linda remarks about (actually, the size of one bone turns out to be no guarantee).

Meanwhile, in the future museum, without a time machine, Professor Onassis arrives with his original time machine, just invented, and decides to settle in this time period: corn dogs are a reality at last. A determined Candace immediately borrows it to go to the day of the roller coaster to bust Phineas and Ferb—it was the very first day of summer vacation.

Now events in the present appear as originally seen in Roller Coaster. But just as Candace screams at the barren pillar where the rollercoaster ad once was, future Candace takes Linda outside so she can see the actual rollercoaster for herself. Linda freaks out and starts making calls to get Phineas and Ferb rescued—they’re really busted. This has the catastrophic side effect of causing the helicopter which Perry had used to lift the giant magnet to change course, making Perry miss with the grappling hook and get hit by the giant ball of tin foil while Doofenshmirtz jumps to the lower roof of his building, exclaiming, “I’m alive!”.

Linda yells at Phineas and Ferb for their reckless acts, and future Candace returns to her time, satisfied with her work. However, that joy is short-lived once she notices the bleak world she's returned to. It seems that Phineas and Ferb getting busted caused outraged parents to overreact and remove anything creative and fun, eventually child-proofing children. This, and Perry being in a body cast for 18 months, allowed Doofenshmirtz to get the upper hand—he has become emperor Doofenshmirtz! Among his various edicts are that everyone must wear lab coats, change all their names to Jo(e) (the easier for Heinz to say “How’re ya doin’, Joe?”), and they must bask in his glory whenever passing his statue. Candace then must return to the present, to stop her slightly younger self from barging into the supermarket to bust her brothers. She succeeds with the time machine (now removed to a junkyard—it arrives back as the first item of junk is deposited in a park), and both older versions of Candace hide behind a car to watch events proceed unaltered: now they see how the helicopter snatched that rollercoaster! The Candace who ended up in the dystopia tells her slightly-younger self about the future, and they agree they must stop altering the past.

They rush to the “junkyard” time machine to return to the future, but now it gets smashed by the giant tin foil ball. Figuring Phineas and Ferb are their only hope of returning home, they go to the backyard after Linda sees the boys under the tree but before the tree explodes. Phineas is shocked at there being two mature versions of Candace, and they explain their situations. Phineas points out that, since the bad future will no longer happen, that Candace should cease to exist, which immediately happens: “Oh darn.” Phineas, Ferb, Isabella and future Candace go to the museum to fix the time machine that's still sitting there, and young Candace follows behind. She tries to convince future Candace to come back with her to bust the boys, but she explains that she no longer has any interest in busting them. Disappointed, she tags along in the time travel to the future.

In the future, Candace triumphantly rushes to find Linda, being the only proof she needs to bust Phineas and Ferb. The boys and Isabella follow to maintain the time-space continuum. Linda is shocked at Candace being so young, while the children are shocked at Linda's oldness. Young Candace is disappointed that the boys receive no punishment, but settles for the fact that the boys were, indeed, busted. At the museum, before returning to the present, future Candace gets the boys to promise never to time travel to the future again. Isabella disappears for a brief while, reappearing later in the time machine with a soda. Amanda then mentions how Isabella looks like her aunt, which she takes to mean she marries Phineas, but Candace points out she might marry Ferb—he cheerfully acknowledges the possibility with a sly gesture. The boys go home, and we get a brief look at the hyper-dimensional bumper cars. In the present, Candace declares that, now knowing the boys can be busted, she will never stop trying to do so.

During the closing credits, Isabella travels back in time to just after Phineas decides to travel to the future and stops them by giving them the wood-metal fuser they needed in the first place. Phineas offers her a soda, which she accepts—she vanishes with it. Phineas points out that now they don't need to travel to the future. At all. To begin with.

Songs

 * Second verse of the extended version of Today is Gonna Be a Great Day
 * It's a Charmed Life!

Spoilers about the Future

 * Future Phineas and Ferb are not shown, but they are mentioned.
 * Candace has three children, identical to her own family - two sons, Xavier and Fred, and a daughter, Amanda
 * Some of the plot-line is similar to Back to The Future II.
 * Perry is alive (albeit very old) in the future, still battling Doofenshmirtz... at checkers!
 * Any relationship (Phineas and Isabella, and Candace & Jeremy) is not shown in this episode. It is, however, mentioned that Isabella does eventually marry one of the two brothers - which brother it is is not made clear.
 * The antique shop still exists and is running.
 * Linda has visited Camp David.
 * 30 year old Phineas is in Switzerland to receive an award. Most likely NOT the Nobel Prize since it is awarded in Sweden.
 * 30 year old Ferb is in Camp David. Most likely in an advisory role, since being 30 would be too young to be President(35 years old is the minimum age for president). Also, the President must be American-born, whereas Ferb was born in England.
 * Stacy is the President of Uruguay.
 * The second verse of the full theme song is sung during near the end of the first third.
 * Phineas and Ferb now have an exact age- they are 10 years old in the present.
 * If the current time stream stays the way it is seen to end up going, the only time Phineas and Ferb will ever get busted is 20 years in the future, and nothing will come of it.

Whatcha doin'?
Said by Isabella as she enters the backyard in the present.

Perry's entrance to his lair
None.

Background Information

 * The episode features the second verse of the extended version of the theme song.]
 * Jennifer Stone, Moises Arias and Jennifer Grey were credited in this episode.
 * A clip of this episode was shown at Comic Con 2009
 * This episode aired on September 21st
 * This episode was leaked onto Youtube on the 19th of September.
 * Phineas knows Bowling For Soup and even says the name of the band to Xavier and Fred.
 * This confirms that in the present, Phineas and Ferb are 10 years old.
 * Goof!: On the checkers board Perry and Doofenshmirtz, it shows two checkers side-by-side. In checkers, all pieces stay on one of the two colors the entire game. It is possible, in the future, that the rule has changed, or that's how they play.

End Credits
Isabella travels back in time to just after Phineas decides to travel to the future and stops them by giving them the wood-metal fuser they needed in the first place. Phineas offers her a soda, which she accepts—she vanishes with it. Phineas points out that now they don't need to travel to the future. Ferb says maybe some other time. During the end logos, Candace yells I'm watching you!!

Continuity

 * Future Candace busts Phineas and Ferb when they build their first "Big Idea", the Coolest Coaster Ever, on the first day of summer. She also finds out how it disappears.
 * This is the first episode that the future has few plots of the first episode, Rollercoaster.
 * It's About Time!: The time machine from this episode reappears in this episode, along with the appearance of Professor Onassis, who created the original time machine.
 * It is said by Candace in The Best Lazy Day Ever, Swiss Family Phineas and Spa Day that she will date Jeremy through high school and college and then marry him and have two kids, Xavier and Amanda, which is seen in this episode, along with Xavier's brother, Fred.
 * Future Linda mentions that she's preparing for her Comeback-Comeback-Comeback-Comeback-Comeback-Comeback-Comeback Tour, presumably referring to her Lindana career first seen in Flop Starz. She says that if she does two more comeback tours, she gets a free pie.
 * At the end of It's a Charmed Life!, Doofenshmirtz holds a long note, along with the music at the end, it sounds the same as My Goody Two-Shoes Brother from Tree to Get Ready.

Guest Stars
Bowling for Soup sing the second verse of Today is Gonna Be a Great Day in the future.

Cast

 * Vincent Martella as Phineas (Past & Present)
 * Ashley Tisdale as Candace (Past,Present & Future)
 * Thomas Sangster as Ferb (Past & Present)
 * Alyson Stoner as Isabella (Past & Present)
 * Maulik Pancholy as Baljeet
 * Caroline Rhea as Mom (Past,Present & Future)
 * Kelly Hu as Stacy
 * Dan Povenmire as Dr. Doofenshmirtz (Past & Future)
 * Jeff "Swampy" Marsh as Major Monogram (Future)
 * Dee Bradley Baker as Perry (Past & Future)
 * Tyler Mann as Future Carl
 * Jennifer Stone as Amanda
 * as Xavier
 * Moises Arias as Fred
 * Jennifer Grey as Librarian (possibly Joe)
 * Bowling For Soup as themselves