On and off camera, actors Ginnifer Goodwin and Allen Leech are extremely charming people. When they're together, the effect is magnified. This shouldn't be a big surprise — Goodwin rose to fame playing a literal Disney princess (Snow White/Mary Margaret) on ABC's Once Upon a Time and Leech stole hearts on Downton Abbey as rebellious Irish chauffeur Tom Branson, who won over the aristocratic Crawley family's youngest daughter, Sybil.

The two have paired up for Constellations, Nick Payne's Olivier-nominated play receiving its Los Angeles premiere at the Geffen Playhouse. Leech, in his U.S. stage debut, plays Roland, a beekeeper, and Goodwin, making her L.A. stage debut, is Marianne, a quantum physicist. The pair's lives intersect in a dizzying array of vignettes that find them living out the variable facets of parallel lives in alternate universes in an attempt to probe the cosmic forces at play when it comes to finding (and losing) love. Shifting rapidly between scenes that can be altered by a single word or turn of phrase, the two delve into what's perhaps the most common existential query: “What if?”

Before being cast, Goodwin had been feeling an intense “homesickness for theater.” She realized she had fallen out of touch with the scene, so she called up the Drama Bookshop in New York and had boxes of plays shipped to her house. She fell in love with Constellations, and when she read that the Geffen would be doing it, she begged her reps to get her in a room with director Giovanna Sardelli. “Given the themes of the play, there was something uncanny about all that coming together,” she says.

Leech came on board after Goodwin was already in place; in fact, he heard about the production through Goodwin's Once Upon a Time co-star Jennifer Morrison. He had seen the play in its original run in London's West End and had wanted to be a part of it ever since.

Though they came to the project individually, Goodwin and Leech are a captivating pair who seem as if they've worked together for years rather than a few weeks. They radiate warmth even over the phone, regularly finishing each other's sentences and breaking into peals of laughter. Goodwin says the challenges of the play feel like “doing gymnastics for a straight hour and a half”; without missing a beat, Leech proclaims, “Yeah, it's actually Cirque du Soleil's version of Constellations.” While Goodwin waxes poetic about the centuries-old tradition of theatrical storytelling, Leech jokes about how the first actor must have earned eye rolls from his friends.

Both face the challenge of readjusting to theatrical performance after spending the past several years working primarily in television but agree that it's something they've relished, particularly the luxury of a multiweek rehearsal period and the space to experiment. “The really lovely and almost decadent thing we get to do is we get to play for four weeks,” Leech says.

Goodwin notes that the experience has highlighted the immediacy of stage acting. “[Film and television] is an editor's medium, and so the onus is off of you to actually deliver everything at once,” she says. Leech adds, “There's such a vulnerability when you're onstage. We're kind of protected within when you're on TV and film. There is that rawness being onstage, just you're here and they're here and we're going to do this.”

Goodwin says this both thrills and scares her: “There's an authenticity of theater that can be felt, and there's a lot of pressure in this one, in one go, to tell a story with utter truth.”

Beneath their easy banter and giggles is a sense of deep trust and mutual respect. The two actors have only one another — there are no props and minimal sets, and neither leaves the stage for the entirety of the 90-minute intellectual maze of the play. “This is an insanely rewarding experience because we are actually able to go there because I do trust Allen, and I know he makes me a better actress, so I don't need 87 other cast members,” Goodwin says. Leech echoes the sentiment, saying, “When you're lucky enough to work with someone and feel that you have to up your game because you see what they're bringing to the table, that's what I feel every day with Ginny.”

The two admit that the play's structure, where scenes replay with a hair of difference and universes shift abruptly, has proved challenging. “It is impossible,” Goodwin says of learning the lines and keeping the sequences straight. “People think of Shakespearean language as being very challenging, but the truth is you have so much to rely on because there is rhythm and rhyme, and there are rules to his structure that make it actually really easy to memorize for a lot of his plays as if they are songs. But what we have here in little repetitions and just slight deviations, it's a real mind fuck.” Leech says the trick is to lend each scene a distinct “emotional signature” to keep the subtle variations straight.

Goodwin is no stranger to parallel universes. As Snow White/Mary Margaret on Once Upon a Time, she often coexisted in separate worlds, but the character's qualities remained consistent throughout. “This is a bit more of a stretch because most of these universes don't line up with other universes in the play,” she says. “The characterizations only deviate slightly because the characters are coming to the table with different past experiences, but only slightly different past experiences.”

Though the scientific consensus is that multiverses do exist, we can't consciously experience them. Actors, however, lead parallel lives in alternate universes by the very virtue of their profession. “What we do for a living does involve our living parallel universes all the time,” Goodwin says.

Leech adds, “What if I had been this or done this or made this choice? We do get to act them out, and that's the beauty of it. We all have that Sliding Doors moment in life where you think, 'Imagine I had said that,' or 'Imagine I had called that person,' or 'What had happened if I'd been there four or five minutes earlier, or a second earlier?' And that's what this play examines.”

For Goodwin and Leech, it's given them the opportunity to reflect more deeply on this possibility and their ability to live so many lives through their work. Goodwin joyfully says there is another life where she's a literary editor, while Leech jokes, “I hope somewhere there's a parallel universe where I'm a much better actor.”

CONSTELLATIONS | Geffen Playhouse, 10886 LeConte Ave., Westwood | Through July 16 | geffenplayhouse.org

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