Amy Poehler, Aubrey Plaza and Parker Posey

Parker Posey had been waiting a good long time for Amy Poehler to call about Parks and Recreation.

"It's funny, when it first came on I was really hoping that Amy would ask me to be on this show," Posey said, recalling that she and Poehler had been at the 2009 Sundance Film Festival to premiere the comedy Spring Breakdown just months before the debut of Parks and Recreation. "Then I went through a period when I stopped watching the show because no one was asking me to be on it. But then I thought, 'That's dumb!' and I started back up. That's when I got an e-mail from Amy!"

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"She said, 'You'll play my nemesis! We get to fight in a garbage dump!'" Posey said. "I remember reading that and thinking, 'Dreams do come true.'"

Posey will channel her inner mean girl in Thursday's Nicole Holofcener-directed "Eagleton," an episode in which Leslie reunites with her former colleague Lindsay (Posey), who has gone on to become Leslie's counterpart at the parks department of the affluent neighboring town of Eagleton. When Leslie discovers that Lindsay's staff has built a fence around a shared park to prevent Pawnee kids from using it, she finds Lindsay a changed woman.

"Lindsay went to the next town and became this fabulous, preppy, horse-riding poster child. She lives the country club life now," Posey said. "They used to be friends, but now Lindsay is very condescending to Leslie."

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To make it to the set in time to film her episode back in November, Posey flew in just hours before from Boston, where she had just wrapped work on a small film. Between scenes, the actress explained that she felt a bit cloudy because "someone was singing karaoke at the Chateau Marmont for so long and I missed my wake-up call."

But on set at the Toluca Lake Sports Center, no one could tell. Even after several takes of an exchange between Leslie and Lindsay at Eagleton's fancy town hall meeting — Leslie: "Nice outfit. What? Were you just in the stables?" Lindsay: "Yes, I was just  in the stables," — Poehler is still trying to hold down giggles. "Parker's just so funny, and such a good improviser," she said.

"Frankly, she can be super mean and cold and kind of bitchy and everything, and yet you still totally like her," executive producer Mike Schur said. "You can tell she's got a warmth somewhere down deep, and that's exactly what we needed."

"She really should have been sleeping and taking wellness formula to ward off illness, but it was incredibly fortunate for us that she such a trooper," he added.

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Aside from watching the pair go to battle for the park, viewers will find out why Lindsay left for Eagleton, while Leslie stayed. "It's interesting that Leslie's got very little regret about not making that step, especially being as ambitious as she is," Poehler said. "You'll find out specifically why in the episode, but Eagleton's not her crowd. They don't need any more help. Leslie's got more of a broken bird syndrome."

Will Lindsay find her way back to Pawnee? Posey said she'd love to come back to the show. "I was a fan first," she said.

"I love the tone and the spirit of it. It's a show that looks at this community with an intelligent eye that's both humorous and loving -- and not mean. I like that it's smart and silly at the same time."

Parks and Recreation airs Thursdays at 9:30/8:30c on NBC.