Mackenzie Davis costars in the film, in theaters April 20

Credit: Kimberly French/Focus Features

The comedic minds behind Young Adult are teaming up again with Charlize Theron for their new film Tully — and PEOPLE has the exclusive first look!

Director Jason Reitman (Up in the Air), screenwriter Diablo Cody (Juno) and Theron are back together again for the first time since the 2011 comedy.Their new film tells the story of a young mother named Marlo (Theron), who is gifted a night nanny by her brother (Mark Duplass).

While initially skeptical about having help, Marlo eventually forms a unique bond with the “thoughtful, surprising, and sometimes challenging” young woman named Tully (Mackenzie Davis).

“Marlo is a woman who tries her best to keep up with the demands of being an attentive mother, a loving wife, and maintaining at least some self-identity through it all,” Theron, 42, tells PEOPLE of her character. “But at the end of the day, she’s human, and she drops the ball a little. Or a lot.”

As for her character’s new nanny, Theron says, “Tully watches her newborn overnight so that Marlo can get some sleep, and she becomes a surprising source of therapy and friendship for Marlo and she shows her what life can be like outside the mom bubble. But Marlo starts to realize Tully is not all that she seems.”

Credit: Focus Features

A mother of two, Theron says she drew on personal experiences to play Marlo. “When you’re told you need to look tired and overworked for a role, it’s not hard to remember what those first few months with a newborn are like,” the Oscar winner says.

“Your life is not your own at that point, and I really did identify with Marlo in that it’s tough when you realize that your life will never be the same when you have kids. It’s rewarding of course, but it doesn’t change the fact that those sleepless nights and ever-expanding to do lists really take a toll on you.”

Having that real-life experience played a major role in Theron taking on the role. “I don’t think I could’ve done this film without having experienced motherhood yet, so this film came at the perfect time for me,” she explains. “There’s so much pressure on parents to balance everything in their life so perfectly and to do it with a smile. So I wanted to tell a story that shows parents, ‘Hey, life is a lot harder for us, and it’s okay if you have to get help.’”

Reuniting with Reitman also factored into why Theron signed on. “Working with him again felt like picking up on the last day of shooting Young Adult, just with a different film and character this time around,” she says. “Our relationship has been so solid and consistent all these years. He’s not afraid to tell stories about real women with real flaws — things that are sometimes uncomfortable for people to acknowledge.”

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Reitman was also excited to join forces with Theron and Cody again. “There are few women who look more fearlessly into life’s dirty little secrets and find a way to make them funny and I’m just so damned lucky to work with them both again,” he says.

Davis, who recently appeared in Blade Runner 2049, calls Tully “a pretty unflinching look at motherhood — good and bad — that I found really unique and funny and beautiful.”

Tully hits theaters April 20.

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