Olney Theatre's production of David Hare's turbulent family drama, "The Secret Rapture," has much to recommend it. But right at the center of the whirlwind, it also has a glaring weakness that threatens to undo all the good work being done elsewhere.

The trouble lies with actress Carolyn Swift, who just isn't up to the demands of playing Hare's provocative heroine, Isobel Glass, who runs a small design firm in cutthroat London. Isobel's goodness -- her glistening honesty, her sense of morality, her stubborn refusal to compromise -- makes her a puzzlement to her family, not to say an outright oddity in the self-centered England that Hare attributes to Margaret Thatcher. Indeed, by adhering so tenaciously to her ways, generous as they are, she elicits the scorn, the abuse and even the murderous fury of those around her.

Goodness, as Swift renders it, however, tends to be moist and simpering. Her melting eyes suggest that she is perpetually surrounded by a litter of cavorting kittens. Her nobility is that of the Girl Scout, helping an old lady across the street. And she sentimentalizes bravery, reducing it to a quivering lip, a jutted chin and vague looks of martyrdom.

If Hare's drama is not to seem wildly lopsided, there needs be far more fullness and vigor to the character. At Olney, Isobel is all too easily upstaged by the creatures who are besieging her, exploiting her or throwing up their hands in exasperation and claiming they don't understand her for one minute. Since director James Petosa and his supporting players have easily found what's fearsome and alluring in human duplicity, you'll watch with some fascination as the sharks circle in "The Secret Rapture." I'm not sure you'll care very much about their prey, though.

The author of such plays as "Plenty" and "The Map of the World," and the recent film "Strapless," Hare contrasts Isobel with her crisp sister Marion, who is a minister in the Thatcher government and embodies its rampant materialistic spirit. ("God, how I hate all this human stuff," she snaps impatiently, when family matters hit a snag.) The two are brought together by the death of their father, a second-rate bookseller, and the problem of what to do with their stepmother, Katherine, a vulgar alcoholic no older than they are.

Isobel agrees to take Katherine into her firm, largely out of loyalty to her deceased father. Thereupon, her woes begin to accumulate. In an unwise expansion bid, she loses control of the company to Marion and her husband, a religious fundamentalist who boasts, "We try to do business as Jesus would." When Isobel attempts to disengage herself from her lover, an artist in her employment, he turns into a pleading wreck, then a gun-toting madman. Finally, for all the concern she lavishes on her trashy stepmother, her rewards are insult and betrayal.

Hare makes it abundantly clear that this society refuses to acknowledge the powerless. And since Isobel's generosity is perceived as a kind of surrender, she doesn't stand much chance of survival. (The play's title, in fact, refers to the religious ecstasy said to be experienced by the faithful at the moment of death.)

But you get the distinct feeling that something about Isobel herself -- call it a thirst for mortification -- collaborates in her own destruction. Although neither the play nor this production elucidates the notion, the woman is recklessly good. Much as she merits your sympathy, you also want to shake some sense into her. I had the same reaction to the original 1988 London production and I'm now beginning to wonder if Hare isn't really of several minds about the character he presumably prizes for her virtue.

Swift's performance is no help on that count, being as unambiguous as it is artless. You can't overlook it, but at least the other cast members provide some potent reasons for looking away much of the time. As Katherine, Jennifer Mendenhall is an unapologetic minx in sprayed-on dresses. But she's also a petulant kid, desperate to find something worthwhile about herself. Mendenhall mixes up the two sides mesmerizingly.

As Isobel's lover, Leland Orser's escalation from low-key nice guy to raving maniac is no less compelling. Karen Trott portrays Marion with snippy superiority, then gives in to the fear that motivates so much officiousness: Everywhere she sees human passions spiraling frighteningly out of control. Even her seemingly bland businessman husband (John Neville-Andrews) is not the cipher he seems. The emotional nooks and crannies are deftly explored.

Russell Metheny's sets and Daniel MacLean Wagner's lighting impart a stateliness to this tangled tale, although I can't say that Catherine Adair is doing Swift any favors by dressing her in flowing white gowns indicative of sainthood. At one point, the actress even trails a long white scarf, the ends of which are tinted blood red.

What is it about Isobel? Why does her goodness bring out the worst in others? Everyone wants to do her in. Even the costumer.

The Secret Rapture, by David Hare. Directed by James Petosa. Sets, Russell Metheny; lighting, Daniel MacLean Wagner; costumes, Catherine Adair. With Margo Hall, Jennifer Mendenhall, John Neville-Andrews, Leland Orser, Carolyn Swift, Karen Trott. At Olney Theatre through July 8.