"What did he know and when did he know it?" is an oft-repeated question these days, but its potential power as a political weapon can't compare to its piercing ability when deployed in personal relationships. Getting to the heart of Watergate or the war in Iraq might be a good idea; in matters of the heart, some secrets are better left locked away.

That Stephen Belber's absorbing if unsteady new play, A Small, Melodramatic Story, which the LAByrinth Theater Company is presenting at The Public Theater, is set in and around Washington, D.C. is not accidental. For the four characters Belber has set orbiting around each other, the tight lips and more tightly locked file cabinets of government's highest levels are as integral to their lives as their loved ones. And the information that's released - or kept classified - can mean the difference between a lifetime of happiness and decades of despair.

The power of knowledge to create and destroy with equal facility is familiar territory for Belber: In his play Tape, he showed how the lies and admissions surrounding an off-handed sexual confession could rot the foundations of a friendship; in Match, which premiered on Broadway in 2004, one character's search for the true identity of his father caused a ripple effect upending three lives forever.

Those plays, however, examined their issues in rather abstract emotional terms. Here, Belber doesn't shy from the disastrous havoc the seemingly innocuous "need to know" can wreak. This uncompromising, unflattering dissection of romance in the Information Age is unquestionably Belber's most meaningful and affecting play.

At its center is O (Quincy Tyler Bernstine), a social worker nearing middle age who's never recovered from the apparently senseless death of her husband Burt six years earlier. What lured him out into the street at 3:00 in the morning? Was it merely a lapse in judgment? Some variation of Gulf War Syndrome (he was a distressed veteran who returned changed from the first Gulf War)? Or something even more insidious?

O's uncertainty has all but sabotaged her life, as well of that of her friend Keith (Lee Sellars), who's kept a not-so-secret torch burning for her for years. She can't return his advances, but does at last relent in allowing him to search the vast stores of information at his disposal (he "files knowledge" for a living) to learn the truth of Burt's death. Keith also inadvertently introduces O to his boxing partner, Perry (Isiah Whitlock, Jr.), and the two hit it off.

But as their relationship progresses, Keith unearths secrets about Perry that send O into a new tailspin: Can she trust Perry to tell her what she needs to know? Can she trust Keith, who wants nothing more than to move her into a permanent place in his bed and his life? Are anyone's motives - even O's own - for hiding or revealing anything ever really knowable? Should one even try?

That's Belber's ultimate destination, and despite Lucie Tiberghien's smart direction, he can't arrive there without stumbling a bit. Keith's role as a like-it-or-not information dispenser too often feels like a device rather than an organic part of his personality. Worse, the dueling halves of his character, the knower and the seeker, are never really reconciled, leaving Keith's journey feeling more incomplete than the other characters'.

If this prevents the play from satisfying as fully as it otherwise might, Sellars takes it as far as he can, and excavates every layer of Keith's psyche to explain how his thirst for knowledge and his thirst for O are, in fact, one and the same emotion. This makes Keith so sympathetic and understandable that his successes and failures at manipulating those around him become the guideposts by which O and her actions must be judged. This makes so much sense, it's hard to imagine Keith played any other way.

You thus appreciate Bernstine's work even more, as she's made O Keith's effective opposite: He likes things smooth, she likes things rough, if not as rough as they must become for her to atone for her faithlessness. While bearing the brunt of the play's comedy and tragedy, Bernstine never falters in mining O's flawed, heartbreakingly human notes. Perry is mostly reactive (another minor flaw in Belber's writing) and at times radioactive, but Whitlock invests him with an ingratiating grace and a smoldering sense of humor that tame his occasionally threatening fires.

The only casting misstep is Carlo Alban, who plays Cleo, a young Latin American man dangerously intertwined with the others' lives. While Cleo is as wounded as O, as scheming as Keith, and as unhinged as Perry at his worst, Alban never hints at these complexities until they emerge full grown at the show's climax, suggesting until then little more than a sleepy indifference to the world around him. (Alban played three-quarters of his role with half-closed eyes at the performance I attended.)

Yet Cleo is crucial, as he's the living, raging proof of the power of truths and lies have to build and ruin lives. Alban's failure to keep this uncomfortable but undeniable assertion at the forefront of A Small, Melodramatic Story is the regrettable cipher in a play fueled by - and filled with - unexpected, exciting ones.

A Small, Melodramatic Story
Through November 5
Public Theater, 425 Lafayette Street
Tickets online and current Performance Schedule: Theatermania