"A MERCY," by Toni Morrison, Knopf, 176 pages, $23.95

Toni Morrison's books are epics of the failure of the country's conscience. "When I began, there was just one thing that I wanted to write about, which was the true devastation of racism on the most vulnerable, the most helpless unit in the society — a black female and a child," she told The New York Times in an interview.

Almost 40 years into her career, a black female child is still at the heart of her writing. In the Nobel Prize-winner's first novel in five years, "A Mercy," she goes back further in history than her most searing and poetic novel, "Beloved," to look at the foundations of slavery in an America "before it was America."

The chances for mercy to thrive in a new land are weighed on a small farm in New York. Four women who were acquired by farmer-turned-trader Jacob Vaark in various ways — marriage, purchase, repayment of debts — have forged an unlikely family, partly out of proximity but also out of a deep, thwarted hunger for motherhood — either to have one or to be one.

There are also two indentured male servants (whose contracts never seem to end), so the farm is a small collective of every type of servitude possible years before the country turned exclusively and implacably to the enslavement of black Africans. This might seem like a contrived setup for a morality play, but once Morrison's writing takes over readers will not notice.

"White men, by and large, are not powerful figures in black women's literature," Morrison remarked in the same New York Times interview. While the women are definitely the center of "A Mercy," Morrison offers a more complicated portrayal of a white male in Jacob Vaark.

An orphan himself, Jacob has a tendency to collect strays. His wife, Rebekka, came over from England when she was 16, essentially sold by a family that didn't want to feed her anymore. Her "prospects were servant, prostitute, or wife, and although horrible stories were told about each of those careers, the last one seemed safest."

Given her low expectations, Rebekka is thrilled with Jacob (and he with her). They seem destined to have a happy marriage, until their children all die, one after another, leaving Rebekka "unleavened," in Jacob's words.

Her companion, Lina, is an American Indian whose tribe was destroyed by disease when she was a child. She was raised by Presbyterians until "Christianized and capable," they sold her to Jacob.

The final member of the household is Sorrow, a seemingly vacant girl who escaped from a shipwreck and who Jacob agreed to take in exchange for some lumber.

While in Maryland in 1682, seeking repayment on a debt, Jacob visits the tobacco farm of a Senhor D'Ortega. D'Ortega has no money, so he offers him another form of portable wealth: a slave.

Jacob initially recoils but ultimately accepts a little girl named Florens when asked to by her mother.

"From his own childhood he knew there was no good place in the world for waifs and whelps other than the generosity of strangers," Jacob reflects. "Even if bartered, given away, apprenticed, sold, swapped, seduced, tricked for food, labored for shelter or stolen, they were less doomed under adult control."

So he brings Florens back home to his wife, the act of "mercy" of the title. But Florens never recovers from being "by her mother," whom she believes chose her baby brother over her.

And the act of acquiring her opens Jacob to the possibility of doing more than just dabbling in slavery.

While repulsed by what he sees as the overindulgence and excess of the D'Ortegas, Jacob becomes determined to acquire the same kind of house and trappings, and another trader explains how: the sugar plantations of Barbados, where the labor is free and infinitely replaceable.

At the Vaarks' farm, Lina mothers Florens, and Rebekka is mildly amused by the little girl who "however slight, any kindness shown her she munched like a rabbit."

If the quality of mercy on display here is dubious, the blessings are even more so. By 1690, Jacob has just died of smallpox, never having had a chance to live in the mansion he spent years constructing, and Rebekka, still childless, is ill with the same disease.

The now teenage Florens has been sent to find a free African blacksmith who is believed to have healing powers. If Rebekka is dependent on Florens' speed and Lina's nursing, the other three women are in terrible trouble if Rebekka dies. With no mistress, Lina realizes, they will be easy prey.

"They once thought they were a kind of family because together they had carved companionship out of isolation," someone says of the residents of the Vaark farm.

Like a dream deferred, if a mercy is hidden too long, it tends to explode — as Morrison shows in her knockout final monologue. It's a spare, dark fable — and at under 200 pages, a swift, kaleidoscopic trip into tragedy.