Edward Gero, left, and Gabriela Fernandez-Coffey in “The Nether.” (Scott Suchman)

Do depraved acts constitute crimes if they’re solely online fantasies? As the Web is ever more a place to congregate for comfort and community, do we become as accountable for our behavior there as in the material world?

Playwright Jennifer Haley tests our moral grasp of the boundary between what one might entertain in one’s mind and one might commit on a computer in “The Nether,” a startling, chillingly engrossing drama that’s been expertly mounted by director Shana Cooper for Woolly Mammoth Theatre.

Mind you, this is no mere academic rumination about the most degraded impulses explored on the Web. (And it’s not for the young ones, either.) Making her example of some of the most repulsive offenses conceivable, Haley certainly gets you to pay close attention. In “The Nether” she constructs a perverse electronic underworld of the future, rendered even more unsettlingly because it’s a destination of perceptible serenity and beauty. In a virtual Edwardian-Age environment called “the Hideaway,” members of a clandestine group are given the opportunity by the site’s creator (a suitably haughty, lugubrious Edward Gero) to indulge their awful predilections without preying upon a flesh-and-blood child.

For sure, the premise doesn’t exactly sell itself. (“Honey, there’s a new play about child molestation at Woolly. Let’s go!”) And mercifully, the online activities do not extend on the stage to callous and tasteless dramatizations — although we are introduced to a product of the imagination of Gero’s Sims: a young girl, Iris (Maya Brettell), who dwells in Sims’s online “realm.” Iris is a computer creation, designed to be (there’s no other way to put it) defiled by Sims’s clients, who themselves prowl the Nether (the new name for the Internet) as avatars, their identities masked in digital disguises known as “shades.”

Haley, though, appears to have more on her mind here than scandalizing us. As Sims claims about the Hideaway to a detective (Gabriela Fernandez-Coffey) who has the task of locating Sims’s server and shutting down the operation: “They’re only images, without consequence.” (The parallels to the work of the Thought Police in George Orwell’s novel “1984” are not difficult to discern.) And still, the illicit liaisons playing out before our eyes not only feel disconcertingly real, but the playwright also posits that “the Nether” exists in a time when people can shed their corporeal forms and migrate their consciousness onto the Web. So here the question becomes: if there is “consequence” in the minds of those participating in the online practices, are these men more than mere fantasists, and does a society have an obligation, or the right, to stop them?

It’s a troubling can of worms that Haley opens. And the handsome platform that Cooper and her design team devise for the production magnifies our discomfort. In the luminous digitized graphics of the Hideaway, set designer Sibyl Wickersheimer and projections designer Jared Mezzocchi create a diabolically saccharine storybook backdrop for Sims’s unwholesome site. The costumes by Kelsey Hunt complete the impression of a world of dark desires cloaked in civility. Visitors to the realm such as Mr. Woodnut (Tim Getman) appear in the finery of a bygone age; Sims, we gather, understands that virtual pedophiles want to build into their fantasies an air of respectability. It’s all supposedly a harmless, victimless ad­ven­ture.

The performances all contribute convincingly to a demi-monde vision of how, through the easily applied anonymity of the Web, we’re all slowly disappearing into our basest selves. Getman, Gero, Fernandez-Coffey and Paul Vincent O’Connor excel as beings who pass in and out of the Nether, and Brettell offers a fine portrait of innocence subjected to perpetual abasement.

It’s all seriously creepy. I mean, seriously.

The Nether, by Jennifer Haley. Direted by Shana Cooper. Sets, Sibyl Wickersheimer; costumes, Kelsey Hunt; lighting, Colin K. Bills; original music and sound, Eric Shimelonis; projections, Jared Mezzocchi; dramaturg, Kirsten Bowen. About 90 minutes. Tickets, $35-$78. Through May 1 at Woolly Mammoth Theatre, 641 D St. NW. Call 202-393-3939 or visit woollymammoth.net.