Newly pregnant and newly ensconced in a not-quite-fully-renovated cottage in the English countryside for her summer holiday, Becky (the radiant Greta Gerwig) is a bit at loose ends. Her husband, John (Jason Butler Harner), is absolutely thrilled about the baby—almost a parody of a concerned father-to-be with his baby books and pregnancy plans and absurd protectiveness. He wants Becky to eat right—no shopping at the Tesco supermarket when there’s a local farm-based butcher in town; no soft cheese—and rest up and exercise—but not too much, and she might want to think twice about that bicycle she’s so anxious to buy so she can explore the countryside—and consider every choice she makes, to ensure she has a perfect pregnancy and they wind up with an even more perfect child.

He’s so protective, in fact, that he’s afraid to touch or even think about his wife sexually while their child is “in there.” Which is a problem, because (not to put too fine a point on it) Becky’s hormones are afire, and she’s absolutely desperate for sex. She’s almost relieved to find John’s porn collection—which he’d supposedly thrown away—in a box in the attic…until it ends up getting her even more excited, and having no effect at all on him. So when John is away on business and Becky finds herself at home with both the widowed local plumber (Max Baker) and a dashing local gentleman who’s dressed as a highwayman (he’s rehearsing for a community theater production), something’s bound to give. (It is no coincidence that the porn films we hear her watching include a steamy plumbing fantasy and a bit of eighteenth-century ravishment.)

Penelope Skinner’s title, The Village Bike, has a double meaning that may be more obvious to a British audience. It’s true, the plot is kicked off by Becky buying a secondhand bike from the highwayman, Oliver (Scott Shepherd), and then proceeds to use bicycle rides as cover for the affair they commence. But the term is also Brit slang for a woman who sleeps with a lot of men: “everyone gets a ride.” And that combination of straightforwardness and nastiness does seem to encapsulate the play’s approach to Becky and her sexuality—for good and for ill.

Fifty Shades of Gray and its successors notwithstanding, it’s rare to see a female character not just eagerly embrace but initiate edgy, rough sex, and to jump with both feet into the not-at-all-politically-correct nature of sexual fantasy—especially in live theater. (Paula Vogel’s Hot ‘n Throbbing comes to mind, though that’s a much darker approach to the topic.) And there’s something wonderful about the way Becky is emboldened—seemingly for the first time, based on some of the things she says to John—to leap fearlessly into this series of increasingly wild sexual adventures, fulfilling fantasy after fantasy for Oliver. At the same time, she’s endearingly awkward at it; she wants to do these things but it’s clearly quite different from the sex she has with John, and Gerwig nails Becky’s mix of tentativeness and abandon.

It’s also refreshing (and hilarious) to see Becky try to talk about her overactive hormones with her over-friendly but well-meaning neighbor, Jenny (Cara Seymour), only to be met with utter incomprehension.

But there’s also a line that’s crossed somewhere in the (overlong) second act, a line where the play seems to shift from investigating her choices to criticizing them—where it starts to seem like she’s less fulfilling her own fantasies than being a prop for Oliver’s, and where she starts to become desperate, degraded by the experiences she’s having. Is a pathetic outcome realistic for an affair like this? Probably—but it’s still disappointing and disheartening to see this character’s brash, goofy spirit squelched.

Director Sam Gold gets nuanced, sensitive performances out of the entire cast; Scott Shepherd’s slow reveal of exactly how and why his character might not have so many fans in the village is noteworthy. But it’s Greta Gerwig’s show to carry, and she is superb, especially given that it’s her stage debut: vulnerable and cocky, funny and touching at the same time, and beautifully grounded in her physicality. It’s a little troubling to see where the play takes her character—but it’s well worth watching Gerwig go there.