The Flynn-Fletchers' neighbors have relatives visiting who bear an uncanny resemblance to Candace, Phineas, and Ferb. In fact, older sister Mandy has two younger brothers, Thaddeus and Thor, who drive her crazy with their ambitious projects. Although Candace and Mandy initially bond, they soon compete, urging their brothers to build the best backyard fort. Meanwhile, Perry finds himself in the middle of Dr. Doofenshmirtz's family reunion where Dr. Doofenshmirtz tries to win the annual kickball tournament with the Kick-inator.
"'cuz there's no way you're gonna lose to a couple of lame-os and their loser sister!!"
She literally throws them into the kitchen.
"WHAT? "Have you lost your minds?!"
"You've completely humiliated me in front of everyone!"
"But Candace, this --"
"Phineas, all summer long, you build the most amazing things and the one time I reach out to you as a sister, the one time I count on you, you give me this?!"
"But Candace --"
"No, just leave me alone! Excuse me!"
Phineas and Ferb's real fort/Doof loses[]
"Ladies and gentlemen, topping our fort is a homage to old-school construction!"
"And now for the rest of it!"
The real fort is revealed!
The kickball bounces off the fort...
...and it lands right back in Roger's hand.
"You're out!"
"
"Well, here's the foyer. All imported marble, by the way."
"Here's the bowling alley...
"Pool..."
"Telescope..."
"Terracotta army room..."
"JET-ENGINE WIND TUNNEL!"
"And scoring stage with 40-piece orchestra."
"We don't, however, have a licorice dispenser. That was a nice touch."
(No response)
"Nice going! You broke their brains!"
Epilogue: The boys are better[]
"Well, Candace, as much as I hate to say this..."
"Your brothers are the best!"
"A ten-story addition with a swimming pool!? Ugh! Why didn't you think of that?!"
"Could it be true?!"
Candace sees the boys' real fort!
"I'm looking at it!"
"When I said 'Throw these in the kitchen', I didn't mean it literally!!!"
Ferb presses the remote...
...and the fort begins to descend into the ground.
"Ooooh, I just felt a disturbance in the cup-stacking universe."
"I think my record's been broken."
"Mom, I've been trying to tell you all summer! They make these amazing things! Look!"
"Hey, Mom! We built a fort!"
"Isn't it great? The boys are starting to take an interest in building things."
Candace faints.
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