In Shakespearean terms, the only real difference between a comedy and a tragedy is the ending. If all ends well, it’s a comedy. If your two teenage lovers kill themselves because of a simple misunderstanding, it’s a tragedy. The Lovers, a remarkable film, walks the line between the two genres magnificently. As we watch its middle-aged married couple rekindle their flame and snuff it out, and then repeat the process all over again, we don’t know if we’re supposed to be laughing or crying, and it’s not until the final shot that we’re sure if it’s a comedy or a tragedy.

As their marriage dissipates, Michael (Tracy Letts) and Mary (Debra Winger) have found respite from their humdrum lives in the arms of others. Mary has a good thing going with Robert (Aiden Gillen), a sexy and sturdy writer, while Michael is mixed up with the volatile Lucy (Melora Walters). Neither Michael nor Mary knows about the other’s lover, but they have coincidentally each promised their paramours that they’ll end their marriage in a week, just after their college-aged son returns for a visit.

It feels like a promise that has been made before, but the seriousness of the deadline causes Michael and Mary to instinctively reassess their marriage. They become caught in a powerful sexual vortex; in short, they can’t keep their hands off each other, and they find themselves doing things in the bedroom they haven’t done in years. Suddenly, their marriage is more fresh and exciting than their now-stale affairs, causing a complex set of moral questions, such as: Is it possible to cheat on your mistress with your spouse?

It would have been easy to make The Lovers a silly comedy about old folks behaving badly, and perhaps even simpler to produce a fiery domestic drama. At moments, it tilts toward each of those, but director Azazel Jacobs seems steadfastly committed to keeping his viewers off-balance. He bathes every domestic scene in shadow, implying forbidden activity in every corner. Just when you’re expecting a confrontation, the film somehow elicits a giggle. The engaging score by Mandy Hoffman reflects its ethos of unpredictability, shifting so frequently between major and minor keys that we can never even settle on a feeling, allowing us to ride the waves of its characters’ passion.

These aesthetic choices are so bold that they occasionally threaten to overpower the film’s marvelously subtle lead performances. Jacobs, however, knows when to pull back and let his veteran actors shine. Letts in particular is a revelation. The Pulitzer Prize-winning playwright (August: Osage County) nearly stole the show in last year’s remarkable Christine, but this is his finest performance. From the outside, Michael is an overweight loser stuck in a dead-end job, but Letts slowly reveals his youthful vigor. It’s not just his pronounced sexual appetite; there is a vulnerable passion here, an optimism that succeeds in breathing free against all odds.

As for Winger, it would be tempting to call her performance a comeback, but she has made clear she’s not interested in a conventional acting career. Instead, she is a celestial cinematic event that only appears every few years, forcing us not to lament her absence but to be grateful for her presence. In The Lovers, she sets the passionate and precise tone that permeates the entire film. Her commitment to Mary’s emotional reality is what allows us to be comfortable balancing on that wire between comedy and tragedy. And so we experience The Lovers as its characters live their lives: teetering on the precipice, reveling in uncertainty, and loving every moment of it. 

The Lovers opens Friday at E Street Cinema, Bethesda Row, and Angelika Film Center.