GableStage's production of Cock contains what might go down (pun intended) as the most arousing sex scene you'll see onstage all year. Except you won't actually see it. Contrary to the expectations of its saucy title, Cock is chaste as can be. Physical contact is limited to the occasional embrace of hands in this rendition, and even those moments seem to defy the strict orders of UK playwright Mike Bartlett.

There are no props, and nobody mimes his actions. There is only one sound effect. Three of the characters don't even have names. The set is a purely abstract space, hardly reflective of the kitchens, living rooms, bedrooms, cafés, and subway stations where the action takes place. This is theater of the mind, a play that would sound minimalist even on the radio.

But you could almost feel the entire auditorium grow a few degrees hotter during the play's central sex scene between John (Ryan Didato), an ostensibly gay man escaping a fractious relationship with an older partner, and "W" (Julie Kleiner), a pretty 28-year-old divorcée with whom he strays. Bartlett permits us to hear their thoughts as heterosexual coitus commences, a first for John. The actors describe their actions in vivid — but not pornographic — detail, culminating in an orgasm. All the while, the actors circle around one another, less like humans caught in a moment of passion than animals engaging in a pre-mating ritual. Eventually, they stand side by side, staring at us, their arms never leaving their sides. Technically, a child could watch the scene and be none the wiser to what he just saw, but adults will want a cigarette after it's over.

Cock is an electrifying exercise in audience imagination; we're often asked to literalize what we can't see, to create our own imagery from the ethereal metaphors percolating in its empty spaces. The magical balancing act between emotional openness and physical prohibition is vital to this challenging, self-reflexive play, produced with superb and creative direction by Joseph Adler. Removing from the actors' toolboxes the natural tendency to embrace, to kiss, to shove, to throw each other to the floor in anger or lust, Bartlett and Adler somehow render these movements unnecessary. The actors' delivery and the lucidity of our own imaginations render unnecessary the crutch of physical contact.

John and "M" (Nicholas Richberg) live together, but it's not always a happy coupling. They clearly love each other, but they fight a lot, locked in unhealthy patterns of dominance and submission. They're the kind of opposites who attract; their polarized personalities are best expressed in John's theoretical scenario of a knife-wielding man on the street: "You will step toward him, and I will walk away," he says.

At an emotionally fragile point in their relationship, John meets Kleiner's lovely W, and sparks unexpectedly fly. She seems to genuinely appreciate John and his quirks, which have grown to be ordinary and insufferable to M. Although John falls for her, he's not upfront about his indiscretion, instead inventing a manly, almost gender-bending paramour to soften the blow. The action climaxes in a forced dinner gathering that includes the three players and a surprise guest. There, John is prompted to choose one, and only one, partner.

In his stage direction, Bartlett calls for "no scenery," but Adler breaks this rule, with effective results. The story plays out in a boxing ring designed by Lyle Baskin. Because there is a fourth wall, it's a three-pointed design that perfectly accommodates the love triangle that transpires within it. Scenes transition briskly with the chime of a bell (sound designer Matt Corey's only apparent contribution), and characters divide their time inside and outside of the ring, stepping in to make a point and incite a conflict.

Jeff Quinn's lighting design changes whenever the players enter the ring and a symbolic "fight" begins: The lights suddenly become blaring, harsh, and Brechtian, exposing the warts and all. During intense scenes, the actors' spittle is visible as it exits their mouths, which would normally be a distraction. Here, it fits the director's vision by conjuring great boxing movies such as Raging Bull and Million Dollar Baby, in which bodily fluids escape from the actors in stylized spurts.

Adler's cast is uniformly excellent, all of them Americans speaking with unflagging British accents. Didato makes his character's confusion, indecision, and repressed torment palpable, and Kleiner, though not necessarily resembling Bartlett's buxom, ultrafeminine creation, excellently captures W's warmth and sensitivity as well as her hidden feistiness and well-masked insecurity, even when she seems to be winning the competition for John's affections.

But it's Richberg who towers above both in a bravura performance of a man who is both dastardly manipulative and magnetically attractive. He finds humor in hurtful lines while capturing the vulnerability hidden beneath moments of brash bluster, rooting out all of the hidden meanings. A lesser actor might convey only one side of this complicated character, but in Richberg, we experience every nuanced shade of this messy dichotomy. He's never been funnier ­— and arguably never better.

There is no logical way for Cock to end happily, and Bartlett deserves credit for not scripting a Hollywood ending. John's fateful choice is important, but his decision is less vital than the greater points Cock raises about the increasingly amorphous nature of sexual attraction and gender identity — about the outmoded status of orientations and pigeonholes, of even such a seemingly encompassing label such as "bisexual."

Alfred Kinsey understood in the mid-'40s that we all fall somewhere on a broad sexual spectrum, but culturally, we're still trying to catch up to his research. At one point, a flummoxed John says, "Gay, straight... these words from the '60s sound so old." He couldn't be more right.