If You Were the Last opens with its two main characters, Zoe Chao’s Jane and Anthony Mackie’s Adam, playing chess in a retro-stylized living room while they debate the plausibility of Matt Damon’s 2015 smash-hit The Martian. Would the U.S. government really go through all the trouble — and spend all that cash — to bring home one guy stuck in space? Do you know how many poor people there are here on Earth you could feed with that money? It’s a cute and entertaining conversation that is soon revealed to carry much bigger implications for Jane and Adam because, as it turns out, they are also astronauts stuck in space — the lone living crew members of a self-sustaining space shuttle that, thanks to an electrical malfunction, has been stuck floating somewhere in the solar system for more than 1,000 days.
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However, while The Martian, as well as Gravity, Apollo 13, and other proud members of the “stuck in space” genre, mine their setup for adventurous thrills, If You Were the Last, the debut feature from director Kristian Mercado, has other things on its mind: Mostly sex, intimacy, and the age-old question of whether “love” is nothing more than a science-based chemical reaction or a more magical, nebulous event that only occurs when two people are truly destined to be together. That’s right, despite the harrowing predicament Jane and Adam find themselves in, If You Were the Last is a rom-com. Not only that, it’s a good one — a 90-minute charmer that eschews realistic FX work (the space shuttle itself and the planets outside its windows look to be made out of cardboard and papier-mâché) in favor of putting two actors with fantastic chemistry together in a tight space and letting the sparks fly.

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When the movie starts, the duo have already been trapped in space for going on three years, and it doesn’t take long for Adam to pop the question: “Look, in case you haven’t noticed, we’re doomed to spend the rest of our miserable lives floating around on this ship. So it would be crazy for us not to bang, right?” The man has a point. After all, while Jane and Adam are surprisingly chipper considering their predicament, all the days spent playing chess, watching the same movies over and over, having dance parties, and hanging out with the chickens and goat that serve as their food sources are starting to get a bit old. And while Jane concedes it’s a fair question — “You have the only penis for a million miles,” she admits — she still has some concerns. For starters, they’re both married with spouses who may or may not be waiting on them back home, and Jane, who finds time every day to tinker with the ship’s electrical system, still hasn’t given up on fixing the ship and returning to Earth.

There’s also a bigger problem — the romantic entanglement of it all. As scientists, they can appreciate the fact that sex and human intimacy are healthy and necessary parts of life, but Jane worries what the emotional toll might be if they open that door. The thing is, as the days tick by, a strong emotional bond starts forming between the two astronauts anyway, and the question of whether or not to have sex becomes less a scientific one and more a matter of acknowledging their growing feelings.

It’s all a little cutesy, but ultimately it works thanks to the winning performances from Chao and Mackie. Chao feels like the true lead here, giving a performance that effortlessly swings from endearing to funny to heartbreaking and back again. Mackie’s role is a little more straightforward, but he proves to be way more effective here than when he’s trying to parlay his Avengers status into more standard action/sci-fi junk (see — or rather don’t — 2021’s Outside the Wire). The guy may be the new Captain America, but he might be best suited for playing more laid-back romantic leads. The two are wonderful together, and it doesn’t take long to get the audience invested in their increasingly complex relationship.

The film’s other big win is in the style department. The “homemade aesthetic” that results in the cardboard spaceship carries over to nearly every frame. The ship’s control panels appear to be drawn on with Sharpie markers. All the computer monitors feature smiley faces built out of eight-bit graphics. The furniture on the ship looks to be intentionally at least a half century old. And the movies and music that Jane and Adam watch and listen to all exists on small cartridges that are then loaded into a console like they’re Atari 2600 or NES games. (There’s even a bit where they end up panicked, frantically blowing into one of the cartridges after it stops working — a feeling that any Gen Xer watching should know all too well.) Taken together, it creates a sense of purposeful unrealism that not only fits the tone of the movie well, but also allows the audience to focus on what’s important, namely the blossoming romance between Jane and Adam.

If You Were the Last is also often quite funny. The movie, written by Angela Bourassa, features some occasional blasts of pitch-black humor that lands almost every time. At one point, the ship had a third crew member, Benson, who died and now exists only as a skeleton in a flight suit that hangs out in the living room and who Jane and Adam will occasionally engage in one-sided conversation with. There’s a whole backstory involving Benson that is slowly revealed over the course of the movie, and it only gets funnier and funnier as the full tale is revealed. At the same time, things do occasionally verge on being a bit too silly. The fact that Adam is so terrified after watching Ridley Scott’s Alien that he has to sleep in Jane’s room feels more like a screenwriter’s excuse to get them into bed together than it does an honest reaction from a grown-ass scientist and astronaut. Another small story hiccup comes when Jane points out another reason they may not want to have sex — she could get pregnant. Adam argues that it might not be so bad to raise a child alone on the stranded ship, a viewpoint that honestly seems a bit indefensible, and then points out that Jane is likely sterile now thanks to the radiation she’s been exposed to (which leads to a big fight). Both concerns eventually fade away without the film bothering to address them again in any depth.

Still, these are minor things, and If You Were the Last covers a lot of ground on the way to answering “will they or won’t they?” It then further covers a lot more after resolving that question. (For the sake of spoilers, I’m entirely avoiding discussing the movie’s final act.) But it’s to the film’s credit that, while it ultimately arrives at a place that could be called predictable, it often takes surprising and satisfying routes to get there.

Rating: B

If You Were the Last premiered at the SXSW Film Festival.