The easy step from bigotry and ideological entrenchments to outright madness gets a timely depiction in David Ireland’s Cyprus Avenue at Off Broadway’s Public Theater. Timelier, perhaps, than Ireland or his star Stephen Rea (The Crying Game) could ever have imagined.

Be warned: A child – an infant, in fact – will pay the price for adult madness, and though the Belfast-set drama takes place nowhere near America’s southern border, recent headlines of youngsters caged, literally, in fights not of their making resonate throughout Ireland’s dark allegorical drama.

Cyprus Avenue, directed by Vicky Featherstone and a co-production of the Abbey Theatre and The Royal Court Theater, begins before we, the audience, have a chance to adjust our boundaries, which most certainly is the point. On a lovely, intentionally bland off-white set with a few sticks of the attractive but not overly comfortable furniture of a psychiatrist’s office, a suited man named Eric (Rea) nervously if deliberately wanders to his patients’ chair before the audience stops its pre-show chattering.

Despite the assurances of his psychiatric case worker Bridget (Ronkẹ Adékoluẹjo, exceptional) that the office is a safe space where any question, comment or insight is allowed, Eric quickly puts that notion to the test – and signals to the audience that this play won’t be so safe – by asking why Bridget is black. Only he uses the N-word.

Maintaining her composure without giving an inch, Bridget engages in the question, drawing out Eric’s prejudices – he insists he meant no harm, but was just raised that way – before slowly getting to the shocking reason Eric has been forced to attend these sessions in the first place: Something dreadful has happened to his family.

In flashback, we see just what it was: Eric’s daughter Julie (Amy Malloy) has given birth to a lovely little girl, delighting Eric’s wife Bernie (Andrea Irvine). To say Eric doesn’t share his wife’s enthusiasm is an understatement. A staunch Belfast Unionist and harboring a long-seething hate for the IRA long past the Troubles, Eric is haunted by what he sees as an eerie resemblance between his new granddaughter and IRA hero Gerry Adams. Eric goes so far as to draw a beard and pace eyeglasses on the infant just to be sure, as his sanity unravels – or is it merely ideological hate coming full fruition?

The foreboding, eerie tone of the intermission-less play all but guarantees that Eric’s irrational hate and ingrained need for vengeance against the IRA and little Gerry Adams will land him in that shrink’s office following some bloody, horrendous act. And so it does, graphically and brutally. The Public has placed audience seats on opposite sides of the stage, and with the houselights up we can see the shock and awe on our fellow playgoers as the mayhem ensures, slowly and unsparingly.

But neither Ireland nor Featherstone want merely to show what madmen do when tethers snap, but rather to suggest what causes the snapping in the first place. In Eric’s case, he sees old borders breaking down, the lines between Ireland’s factions that once defined his life and cost him so much. No one cares about such things anymore, his daughter says, unknowingly uttering the worst thing she could possibly convey to a man whose hard-won identity has shattered. If the only way to prove it wasn’t all for naught is to turn back on the spigots of blood, then for Eric, so be it.

The cast is superb, including the Irvine as the wife who lived through the same Troubles as her husband but has emerged with a compassion he can’t muster, and Molloy as their daughter who can’t for the life of her imagine what all the fuss was about.

As a black-clad terrorist wannabe who might just be a figment of Erick’s madness, Chris Corrigan’s Slim is alternatively terrifying and scathingly funny. When he becomes a voice of relative reason, we know he has to go – whether he’s real or not.

But Rea is the star of Cypress Avenue, and chilling in the role, a man so convinced of his rightness that madness seems almost logical. Notions of national and idealogical pride die hard, and take much collateral damage whether in battered, bloody sacks or chain-link cages.