The sleep of reason gives birth to monsters. So noted the painter Francisco Goya in the midst of one of the ugly little wars sweeping across Europe in his day.

In the midst of another ugly little war, this one in our time, a soldier leaves the battlefront badly hurt—so much so that she thinks, on awakening, she has returned from the dead. So Maria Dahvana Headley’s The Mere Wife relates. The soldier does not quite recall the sequence of events that made it so, but she is now pregnant. When she hits stateside, she heads to the woods, to the mountains.

Her wild stronghold abuts a setting of wealth and privilege, a suburban development of high-toned, well-toned men and women and perfect children. The soldier, Dana, gives birth in a fortress of solitude, an abandoned train station deep within a mountain, and the child that her sleep produces is—well, frightening enough that all the creatures who see him take cover.

Gren, he is called. Think Grendel. Being Grendel, if you know the story of Beowulf, havoc must ensue: havoc, death, and unending fear of what lies in the murk, out in the dark. Dana—think Dane, as in Spear-Dane—is afraid. But she is also fierce and protective as a mother will be, just as her counterpart in that development, Willa, is protective of the son who will fall into Gren’s shadow.

Headley, having drawn on Beowulf to make her modern dark fantasy—its title not meaning “mere” as in “easily overlooked” but instead the kind of dark pond that a monster might rise from—is now translating the original Anglo-Saxon poem for publication next year, digging deep into our buried language to revive the story for another generation of readers. But first there is her novel, which, she says, took some time to form: “I started off thinking about something I’ve always been interested in, which is how society makes rules and how people break them. My first book was a memoir about a time in which, for a year, I said yes to anyone who asked me out on a date. That’s definitely not what you’re supposed to do, and while it was comedic, doing what you’re not supposed to do can have a dark side, too.”

It can, and in The Mere Wife, people are doing what they’re not supposed to do right and left, sometimes not even knowing what or why, even as they do as they’re told. “Everyone has a child they wish they hadn’t had,” thinks Willa, the doyenne of Herot Hall, after a particularly fraught fight from which she emerges “a wife, living at last in the sun.” She has nowhere to go but up—or so an admiring neighbor might think, if he or she has failed to note the darkness cast by all those trees and mountains and by all that distant turmoil.

“Beowulf,” Headley says, “is really a book about the suburbs—a place that encroaches on land that used to be wild and that used to belong to someone else. We build a place that we imagine is safe, sheltered, even though it’s just over the fence from that wilderness. Of course, no place is ever really safe.”

Headley, who has collaborated with Neil Gaiman and is well-known for imaginative fantasy novels that sometimes intersect with history, writes affectingly, dazzlingly, of the dangers hidden around every corner. In real life, she’s energetically cheerful. “I love that I get to invent worlds, get to tell stories and make myths,” she says. “It’s an amazing way to make a living.” But Headley also conceives of her work with serious purpose, as an instrument of social change in which she contests war, dominance, classism, sexism, oppression, patriarchy, and avarice—in short, all the things that figure so richly in The Mere Wife.

“Monsters. Some people believe they’re unusual,” Headley writes toward the end of The Mere Wife. “Others know that monsters are everywhere.” You need only turn on the television or turn to the front page to know how true that is. In reaching to the distant past for inspiration, her book holds a mirror up to our time—and the picture that returns is frightening indeed.

Gregory McNamee is a contributing editor.