Mackenzie Davis plays a night nanny hired by Charlize Theron's Marlo in Tully. Picture: Kimberly French, Focus Features

Washington - Who is Brook Busey-Maurio, and what did she do with Diablo Cody?

The distinctive pen name of the Oscar-winning screenwriter of Juno - which sounds like the moniker of a gunslinger in a spaghetti Western - is never mentioned during a phone interview with the writer, who introduces herself by her legal name. (Born Brook Busey, Cody has been married to the actor and producer Dan Maurio since 2009.)

The tattooed wunderkind burst onto the movie scene 11 years ago with the tale of a smack-talking pregnant teenager - and a résumé that included a stint as a stripper. Now 39 and the mother of three young boys, Cody is making the interview rounds to discuss Tully, her third collaboration with Juno director Jason Reitman and the duo's second film starring Charlize Theron.

In the new movie, Theron plays Marlo, a 40-ish mother of two who decides, after the birth of her third child, to hire a "night nanny": a childcare worker who watches the baby while the parents sleep, waking Mommy only for periodic feedings. In the case of Tully, she also cleans the house and bakes cupcakes, like a workaholic elf.

READ: Charlize Theron delivers her most fearless performance yet in Tully

Written 2 1/2 years ago, in what Cody describes as a "postpartum fog," the movie arose out of the writer's personal experience. 

We spoke with Cody about the movie's semi-autobiographical aspects, and its darker themes.

Q: You seem like you might be the "cool mom" at the PTA meetings. Am I wrong?

A: That was what I wanted to be. I had originally imagined myself as the cool mom. The reality, however, as the mother of three boys, is that they need a lot of structure They crave rules, and they crave discipline. So I'm not as cool as I thought I was going to be. I mean, I do drive a cool car: a yellow muscle car.

Q: What make?

A: It's a Dodge Challenger. It's the only cool thing I have left.

Q: How does this movie fit into the continuum of your work with Jason Reitman, which seem to share a theme of growing up, perhaps reluctantly?

A: It's funny, we didn't really realize that these three films were of a piece until Tully was finished. Then it became shockingly obvious to us that we had somehow unwittingly made this coherent trilogy. I think it's because I'm obsessed with the idea of transformation, honestly, and not just the projects I've done with Jason. 

I'm really interested in exploring how we stay connected to who we once were. For me, one of the most powerful images in Juno is actually at the very end of the movie, after she's had the baby and made that decision, and she goes and has this really sweet, adolescent moment with her boyfriend, where they sing to each other. 

Tully writer and producer Diablo Cody at the movie's April 18 premiere. Picture: Eric Charbonneau, Focus Features

Q: You mentioned this film's difficult themes. In your earlier work - Juno, Young Adult - your signature is a sarcastic voice. Sarcasm often is used to mask something painful.

A: Oh, for sure.

Q: With Tully, I feel like you've dropped the sarcasm. Is it coming from a place that's more vulnerable, more honest, less guarded?

A: I do think the movie is more sincere and open, if that's what you mean. Marlo uses sarcasm as a defense mechanism, but we, as viewers, keep getting a peek behind that mask, repeatedly. Maybe I was writing from a more emotional place.

Q: Was that intentional?

A: No. I wish I had the discipline to sit and down and say, "This time, I'm going to try and write something more sincere." I really am at the mercy of my instincts, at all times. I'm always just writing from my gut. What comes out comes out.

Q: You paint a picture of harried parenthood and a sexless marriage. Isn't that a little cliche?

A: Here's the deal. The reason I have images of parenthood being difficult and of mature marriages being unexciting is that it's reality for most people. It's a cliche for a reason. 

I do feel that this movie does something that perhaps other representations of exhausted parenthood do not do. I always feel that there's almost this sitcom approach to showing the difficulties of parenthood. It's like one of those coffee mugs that says, "Mommy needs wine." You're supposed to laugh at it. But we went to a darker place here. It's not "Mommy needs wine." It's "Mommy might kill herself." I think we went somewhere familiar, and then dug a trench under that familiar thing and went straight down.