Phineas and Ferb are sitting under a tree, wondering what to do. Phineas realizes that they will be back in school shortly and they will have to say what they did over their summer vacation. He feels that their time off should be exciting, like a rollercoaster. Remembering the lame coaster they rode at the State Fair, Phineas realizes that's what they should do today: build a rollercoaster.

As their mom, Linda, heads off to do some shopping, Candace runs to her car to confirm that she's been put in charge. Mom doesn't think it's necessary that anyone be in charge, but Candace does. "What if a satellite falls out of orbit and crashes into the house?" It's not likely to happen, so her mom gives her approval and Candace rushes over to tell the boys, "Mom says I'm in charge! ...Conditionally!"
That doesn't bother Phineas. He and Ferb have set up drafting tables and have started working on their "homework". Candace doesn't understand why they would be doing homework during their summer vacation. She heads into the house after admonishing them that they are being watched, and
Tracks for coaster
Added por Gabo 200
reminds the boys that she's in charge, conditionally.

Candace only gets to take one look out the window before the phone rings. It's Stacy, wanting to go to the mall with her. She can't go because she has to watch her brothers. Candace makes sure that Stacy will see if Jeremy is there.

While Candace was talking on the phone, the boys and Perry have been transporting various building materials into the back yard: lumber, steel I-beams, a jackhammer and plumbing supplies. The lion's roar breaks her concentration and she yells at the boys, "Will you hold it down, I am trying to use the phone!". Going back to talk to Stacy, she gets her first hint that something is wrong. Stacy tells Candace that she can see something being built in the back yard from her house.

Candace runs out to the back yard, then stops in her tracks. She looks up and sees a patchwork of pipes and track. Whatever it is, she doesn't like it. She storms off to tell mom, proclaiming that the boys are going down. She repeats it several times and spells it out for emphasis. "We're going to need a blowtorch and some mais amendoim butter" is Phineas' assessment.

As Candace rides off on her bike, Isabella walks into the yard with hearts in her eyes. "Whatcha doin'?" she asks. Phineas tells Isabella that they are building a roller coaster. Isabella then says hi to Ferb, but Ferb only waves his sledgehammer in response. As a man of action, he's busy laying track. He strikes a rivet with the sledgehammer, causing it to bounce and hit him on the nose. Ferb just blinks, apparently unhurt. Isabella had stopped por to invite Phineas to go swimming with her, but he wants to work on the coaster, so she heads off. Phineas then notices that Perry is missing.
Perry is walking nearby alongside the house. He stops and checks to make sure no one can see him. Jumping up onto his rear legs, Perry's demeanor changes. He is no longer a platypus that "doesn't do much". He puts on brown and black fedora, becoming "Agent P". A remote control opens a hidden door in the side of the house and
Agent P steps in and rides the tube elevator down to his lair.
Major Monogram informs him that Dr. Doofenshmirtz has bought "80% of the country's tin foil". Agent P must find out why and stop him. Before Agent P leaves, Major Monogram reminds him to maintain his cover as a "mindless domestic animal". Giving the Major a quick salute, he flies off in his platypus-shaped hover-jet. He exits to the surface through a tunnel. Shortly thereafter, he flies por the boys and pulls his hat down over his face to avoid being recognized.

The boys are taking a break from construction to discuss the seguinte part of the coaster. There will be solid-fuel booster rockets and snakes being released during a corkscrew around the Interstate highway. Phineas heads off to get the snakes while Ferb resumes welding.

Meanwhile, Candace has been trying to get her mom to come início from the grocery store and see what Phineas and Ferb are doing. Linda mentions that she recalls Candace doing the same thing previously, claiming that the boys were training "monkeys to juggle bicycles," but when she came home, "there was a stunning lack of monkeys". Candace persists, telling her about the roller coaster. Linda thinks Phineas is a little young to be a roller coaster engineer.

At that moment, a foreman at a car factory is asking Phineas the same question. After Phineas confirms it, the foreman approves their building permit despite it being filled out in crayon. He offers to give them whatever help they need, so Phineas takes him up on the offer and borrows one of the robotic assembly arms. In short order, the robot arm is mounted to the coaster cars and is laying out track for them.

Nearby, Agent P swings in through a window at Doofenshmirtz Evil Incorporated. Dr. Doofenshmirtz greets him with: "Ah, Perry the Platypus! What an unexpected surprise. And por unexpected, I mean completely expected!" After trapping Agent P, he informs Agent P of his plan to mover the Eastern Seaboard (now covered in tin foil) to the West por using a "Magnetism Magnifier", which will reverse the rotation of the Earth. While Doofenshmirtz is talking, Agent P tries getting free of the robot arms holding him, but then notices a screw on the ground at his feet. Looking around him, he formulates a plan....

Back at the Super comida Stuff Mart, Candace continues her attempts to convince her mom to come home. She sees the poster that Ferb has just put up, but when she gets her mom over to there, two boys took the poster to see if they can get in for a discount. Candace screams when she sees that the poster is gone. Mom informs her she'll be over in the dairy section if Candace wants to "come yell at some cheese or anything".

Phineas and Ferb unveil the Coolest Coaster Ever to the neighborhood kids. The first lift colina climbs up through the clouds, high enough that a bird flies into the track and falls to the ground.
As they start to go up, Phineas is showing everybody how the assento belts work, but he drops it. The coaster comes to a stop at the topo, início of the lift hill, revealing part of downtown Danville far below them. He asks everybody, "You all signed the waivers, right?" They then shoot down and begin the wild ride. There are loops, hairpin turns, and the promised corkscrew. A load of rubber snakes falls on them just before they plunge into a mud bucket. Fortunately, the seguinte section includes a trip through a car wash and they all emerge squeaky clean. seguinte is an "A-A-A-A" portion and a few loops around Doofenshmirtz Evil Incorporated.

Inside, Dr. Doofenshmirtz is still rambling on about how much this scheme cost him. Agent P uses his tail to fling the screw at Doofenshmirtz, "missing" him, making it rebound and hit him in the foot. Hopping around, he accidentally releases Agent P from his robotic arms. Agent P then starts to battle him with wrenches and strikes the same foot of Dr. Doofenshmirtz that the screw hit.

During the fight, Dr. Doofenshmirtz runs over to the Magnetism Magnifier and turns it on, telling Agent P he is too late and it cannot be stopped now. But the Eastern seaboard did not mover to the west, just the tin foil, causing a two-ton ball of tin foil going, at two hundred miles an hora to head straight for them. They both frantically try to turn it off.

At the store, Candace and her mom are at the checkout when Candace hears the coaster going by. She sees the coaster track out in the parking lot and goes back to get her mom so she can see as well.

Agent P is now helping Doofenshmirtz in trying to mover the Magnetism Magnifier, but it will not budge, so he hooks the magnet to a helicopter, causing the magnet to go with it. Dr. Doofenshmirtz is happy about being saved, but is then moved (along with the rest of the tallest part of the building) por the tin foil ball that crashes into it. The magnet attracts the Magnetism Magnifier, which sends a magnetic raio, ray at the track under it, picking up the entire roller coaster.

Candace gets her mother out of the store, but the roller coaster track has already been moved. Since the mom has finished checking out, the two leave, and Candace is now excited because she believes that when they get home, the boys will not be under the tree, therefore proving to her mom that she is right.

Agent P has been riding on topo, início of the magnet and notices that the helicopter has been trailing a plume of smoke from the strain of lifting that much weight. He cuts the cable, making the roller coaster drop to the ground. The kids are still riding this very fast coaster. Agent P jumps onto the coaster with the kids as it passed beneath him. Phineas looks behind him and utters the famous catch phrase, "Oh, there you are, Perry." Instead of seeing Agent P, Phineas sees Perry again, since Agent P put his hat on Isabella a moment before, so he wouldn't be recognized.

The kids reach the broken end of the coaster and ride out into the street, through a construction site and up onto the tail of a passing jumbo jet after a guindaste swings them up into the air. Candace, in the car below, sees the boys on the airplane flying in the other direction and laughs gleefully. Mom says she worries about her sometimes.

The coaster cars finally come loose from the tail of the jet and they fall onto the Statue of Liberty. It bends and then flings them over to Mount Rushmore, where they do some loops inside Theodore Roosevelt's glasses. They then shoot out on a árvore over a Mr. Slushy Burger, then get flung to Paris where they land on a very bendable Eiffel Tower over a croissant stand, finally getting flung all the way into outer space. A satellite passes por the coaster, and Phineas points out that if it falls to Earth, Candace is in charge. At that moment, the coaster plummets to the Earth, picking up speed and catching the nose of the first coaster car on fogo from the friction of re-entry. As they get closer to Danville, Phineas says, "We should've charged more."

Candace and Mom now pull into the driveway and Candace runs out of the car, laughing crazily. She looks into the backyard, and does not see Phineas and Ferb and shouts "yes!" She tells her mom she told her, closing her eyes and extending her hand out to point at the yard, as we hear a rustle of leaves. The mom says "Hi" to the boys, sitting under the tree. She walks into the house, Candace gasping "But" over and over again until Mom pulls her into the house.

The kids now fall out of the tree, all saying how much they liked the ride. Isabella falls out of the tree, telling them how great it was and asking them what they're going to do tomorrow. Phineas says he doesn't know, and Isabella suggests teaching Perry some tricks. Phineas says that platypuses don't do much, followed por Ferb saying his first spoken words in the show: "They're the only mammals to lay eggs". Phineas says maybe he'll lay an egg, and Isabella leaves, saying it really was the best coaster ever and the two make a great team. Phineas replies, saying that he couldn't have asked for a better brother than Ferb, who then burps. Phineas comments that he can smell the amendoim butter.

Phineas then asks what they should do tomorrow, and suggests making a list. Just then the topo, início of the árvore explodes, causing Candace to shout, "Mom!", who responds with, "Give it a rest, Candace!