Sometimes it's the subject matter that most grabs you about a play, sometimes structure, historical context or philosophy. In "The Lady with All the Answers" at the Pittsburgh Public Theater, it's the performance.

Helena Ruoti plays Eppie Lederer, aka Ann Landers, the long-time advice columnist. It's a wonderful, rich, funny performance, full of vim and wisdom.

But first, the play. Ruoti's performance leads us right into the heart of it, not simply because it's a one-woman play but because, even though Eppie has plenty of practical, funny wisdom to share, the play really centers on the person. It's not just her commentary that enlightens us, it's she, herself.

This is because playwright David Rambo has achieved what's relatively rare in a one-person show, anchoring it in a specific time when something significant happens. Sure, there's the usual content of a one-person character study -- the career summarized, anecdotes and witticisms recalled, wise commentary shared. But all the while, on this evening in June, 1975, Eppie is struggling with an intense personal loss.

The play even imagines her deciding, in the course of the 90 minutes we spend together (including intermission), just what to do about it. That may seem a bit stagey, but her real dilemma is how to put into words what she's already decided, and that's a very big deal. Deciding how to say it is practically the same as deciding what to say.

Of course the given is a bit of a stretch -- that she would be discussing all this with such frankness with an unseen audience. But we accept it because (a) it's a convention, and without some conventions there couldn't be any theater at all, and (b) this is transparently just what Eppie did in her career as Ann. As Eppie does on stage, Ann talked directly to her readers about personal things. They were usually personal to them, not to her, but everyone was invited into the circle of intimacy. It's just one small step to transfer this one-woman confessional to the stage.

Notwithstanding the felt reality and Ruoti's performance, much of the show's pleasure comes right from the files of Ann Landers. It isn't just kids who say the darndest things, and apparently they say them freely to advice columnists, in volume: Eppie tells us she got 141,000 letters on sex after marriage (82% said the frequency was down) and even 15,000 on the vexing issue of which way to mount the toilet paper.

She reads us some of the funniest letters, under the pretense of choosing which will go into a book, and we hear some of her pithiest advice. She also notes that she broke the ice in talking about homosexuality and other taboo topics. And she deals humorously with her chief competitor, her twin sister, Dear Abby.

Ruoti's Ann is in command from the start, welcoming us into her home office, moving freely from place to place and subject to subject, allowing the audience to relax immediately and settle in for the ride.

The physical transformation is remarkable, starting with Eppie's matronly, towering mid-century wig. But her midwestern accent is even more transformational, altering Ruoti's mouth and even, it seems, her posture. Ruoti's Eppie is upbeat and smart, a ballsy lady with style, even (in Act 2) in her silk robe and PJs, still fully coiffed and made up, still wearing pearls.

Ted Pappas has provided supportive direction, giving Ruoti plenty of variety and movement on James Noone's spiffy set, a sort of homey Oval Office. The handsome furnishings include a period record player playing period music, with a tilt toward Sinatra, who is, I suppose, timeless. As is Ann Landers, you could say.

Ultimately, the title turns out to have a touching irony. Ann may have all the answers, but Eppie doesn't. Life remains a puzzlement, and in acknowledging that, this one-woman tour-de-force bolsters a brilliant performance with a satisfying play.