On winter nights, Charles Haddesley the Eleventh gathers his five children before the hearth and recites their family's compact with the land. Their ancestor, he says, survived being thrown into a bog, rose with a woman who became his wife, and bound his descendants to the care of a West Virginia cranberry bog. Each generation's eldest son must marry a bog-wife, a woman formed from the peat, to reseal this bond. None of the children can remember where their mother was during these stories.
The novel opens in summer as Nora, 24, discovers unfamiliar orange fungi in the swale, a channel feeding river water to the bog. Her brother Percy, the youngest sibling at 22, finds the torn stems and cannot identify them. Their eldest sister Eda, 33, tells them their father is dying. He insists all five siblings attend the exchange: the ritual in which his body is given to the bog and a new bog-wife rises for the eldest son, Charlie, to marry. Wenna, 27, left the family 10 years ago and must be summoned. Privately, the father instructs Nora to destroy his existing will and write an ambiguous new one. He separately orders Percy to kill Charlie so Percy can inherit and marry the bog-wife. Percy is horrified but cannot refuse outright.
Wenna rides a Greyhound from Illinois, where she has lived since fleeing at 17. She is dismayed by the house's decay and Charlie's gaunt frame; months earlier, a hemlock tree crashed through the roof onto his bedroom, shattering his pelvis and leaving him unable, he fears, to father children. When Wenna visits her dying father, he demands she stay permanently. She refuses, confronting him about their mother's disappearance. He has no answer.
The five siblings carry their father's body to the bog's mouth, where he sinks into the peat. The next morning, Charlie goes to the bog with a dowsing stick meant to guide him to his bride, but nothing happens. He searches for hours until he falls and reinjures himself. The exchange has failed. The family consults the Borradh book, an old manuscript describing the ritual, but cannot determine what went wrong. Wenna implies the failure connects to their mother's disappearance. Eda despairs that they will be the last Haddesleys.
Wenna stays through the fall despite intending to leave. She married a man named Michael in Illinois, but the marriage ended because she refused to have children, fearing it would violate the compact. She begins planning to sell the property. Eda decides to produce an heir herself. Since Charlie's injuries likely left him infertile, Eda has him drive her to a bar in Marlinton, where she sleeps with a stranger. Charlie sells family heirlooms and learns the objects date to the 1890s, not the sixteenth century. A doctor confirms his infertility. When Charlie asks Percy if their father ordered his death, Percy admits he was told but could not do it. Charlie attempts suicide by swallowing cough syrup; Eda saves his life.
During vigils at Charlie's bedside, Percy discovers a recipe in their father's memoirs: instructions for forming a wife from sticks and humus, feeding it one's blood, and burying it for 100 days. At the end of October, Percy assembles a stick skeleton in a deep grave and feeds it his blood. He becomes obsessively vigilant, sleeping outdoors. In the weeks that follow, a voice reaches him through his skin, communicating in primal impulses. The voice multiplies into thousands, and Percy believes his wife is growing beneath the earth.
Nora intercepts a letter from Michael revealing he still loves Wenna. Fearing the letter will draw Wenna away, Nora hides it and begins forging replies in Wenna's handwriting, sustaining a months-long correspondence in which she becomes emotionally invested in Michael's affection.
Charlie visits the library and discovers a photograph captioned "The Maturin folly, under construction," dated 1897. The house was built by Charles Maturin, youngest son of a coal magnate who bought the wetlands from seized farmland. The Haddesley name and noble ancestry were fabricated; the family descended from French textile merchants named Maturin. At a disastrous dinner, Eda announces her pregnancy, Wenna's plan to sell the house is revealed, and Charlie declares there are no Haddesleys, producing the newspaper clipping. Eda orders Wenna to leave. Nora reveals she has been writing to Michael as Wenna, but cannot prevent Wenna from leaving.
A catastrophic winter storm strikes before Wenna can depart. A second hemlock crashes through the house, collapsing the kitchen. The siblings shelter in the stone hearth. In the bog, the underground voices go silent, leaving Percy alone. After the storm, he finds a body at the bog's mouth, clears mud from the face, and spits on the mouth as the ritual requires. The woman breathes. It is not a wife but his mother, preserved in peat for almost 11 years. The stick skeleton in the grave is unchanged; the recipe never worked. The voices were his mother's all along.
The siblings carry their mother to the forest's edge, where she speaks the bog's true history. Sphagnum moss made compacts with other plants, while microscopic organisms called whiptails received the dead and formed wives for Haddesley men. But the Haddesleys' heavy house altered drainage, drying the peat and starving the bog's original species. Their father buried their mother not to kill her but to stop her from changing, believing he could halt the land's transformation. She tells her children the place will not survive without changing, and neither will they. They must make new compacts.
Percy realizes his communion was real, a connection to the living network of the land. His mother presses his fingers into the earth, and he feels the weave of presence return. He shows Nora, who feels herself woven into a vast consciousness. Roots begin growing from Percy's feet; Nora chooses to let the same transformation happen to her. Charlie tries but feels nothing. He crosses out "son" in his father's will, opening the inheritance beyond the male line. He packs the family's books, leaves a note telling his siblings not to look for him, and drives away. At a motel, he registers as Charles Maturin, the family's actual surname, and takes the first shower of his life, scrubbing the bog from his body.
Eda breaks down with Wenna, confessing her terror of failing her unborn child. Wenna tells her she is not alone, and when Eda asks her not to leave, Wenna does not refuse. Wenna writes to Michael, confessing her sister wrote the letters and inviting him to visit. Over the following months, Nora and Percy sleep on the bog meadow with their mother, their bodies gradually transforming into tree-like forms. The kitchen collapses entirely, and they move into the goat shed. Charlie does not return, though he sends envelopes of cash. They read the medieval romance of
Perceval nightly, starting over each time because the ending does not feel like it has ended.
On a warm, moonlit night, Eda goes into labor. Wenna supports her to the forest margins, beneath the three slender trunks that were once her mother, Nora, and Percy. As a contraction crests, Eda digs her fingers into the earth and feels the land braiding her into itself. On the moss-covered ground, above 10,000 years of buried history, she gives birth to a girl. They name her after no one.