The novel opens with a narrator's note that a legend is forming on the west side of the mountains. Before myth overtakes truth, the narrator promises to tell what actually happened.
Homer Smith is a 24-year-old Black man, six foot two with deep black skin, recently discharged from the Army at Fort Lewis as a buck sergeant, a junior enlisted rank. His mother once described him as "two parts amiable and one part plain devil." With savings from thrift, moonlighting, and gambling, he has bought a secondhand station wagon and set out to see the American West, living one day at a time. On a May morning, driving through a valley west of the Rocky Mountains, he spots women working behind a dilapidated farmhouse with no men visible. On impulse, he turns onto the rutted road and offers himself for a day's hire.
The older woman who greets him is Mother Maria Marthe, whom Homer immediately recognizes as the boss. She declares in accented English that God has sent her a big, strong man, which Homer finds amusing and faintly antagonizing. She introduces her companions: Sister Elisabeth, Sister Gertrud, and Sister Agnes. When Homer gives his name, she translates it as "Homerus Schmidt," and the sisters' smiles make him feel welcome. They show no awareness of a color line. Mother Maria Marthe directs him to repair the roof rather than help with the fence, leading him to a well-stocked barn toolroom.
From the roof, Homer notices the remains of a burned house near the barn, its chimney still standing. At lunch he sees a crucifix and realizes these women are Catholic nuns. He observes a fifth nun at the table: the frail Sister Albertine, with large blue eyes. That evening, the nuns try to learn English from a phonograph playing useless phrases. Mother Maria Marthe stops the record, declaring Homer will teach them instead. The nuns break discipline, excitedly pointing at objects for him to name. Sister Albertine, who has a talent for drawing, sketches his station wagon. Homer walks to his car reflecting that these are nice people and the old woman has a shrewd mind.
The next morning, Mother Maria Marthe scolds Homer for sleeping late, and he insists he is neither a nun nor a hired hand. After breakfast, she reveals her ambition: a sketch of a small church to be built on the foundation where the house burned. Homer refuses, saying one man cannot do a contractor's job. Unwilling to leave on a bad conscience, he promises to clean the foundation before departing. He discovers solid granite with a deep, debris-filled cellar and works all day.
That evening, Homer tries to collect wages through a battle of Bible verses. He directs Mother Maria Marthe to Luke 10:7, about the laborer deserving his hire. She counters with scriptures about sharing one purse and considering the lilies of the field, which neither toil nor spin. Homer realizes she never intended to pay him. She then mentions that Sunday Mass in the town of Piedras requires the nuns to walk more than two miles each way. Homer volunteers to drive them.
On Sunday at a café in Piedras, Homer learns the nuns' backstory: They escaped from East Germany, embarrassing their religious Order. The land belongs to the Order because a miserly farmer named Gus Ritter willed it to them; Ritter's sister in Germany belonged to the Order. Ritter's son and daughter-in-law died in a fire caused by a kerosene lamp because Ritter refused to install electricity. The nuns arrived knowing only how to teach, with no school and no English. After Mass, Homer meets Father Gomez, a quiet priest who explains that Mother Maria Marthe wants to create a school for poor Spanish-speaking boys from the city. When the priest asks what Homer thinks about her belief that God sent him, Homer insists God would not send a Black Baptist to a Catholic nun.
That afternoon, Homer fills a pad with figures and feels the idea of building a church elevate him as nothing else has. Mother Maria Marthe joins him and asks quietly whether they can do it. Homer says it would take nearly 4,000 bricks. He plays guitar and sings spirituals for the nuns; Sister Albertine leads them in Latin chant, and Homer finds he can sing along when he hears the Latin words as pure sound. He walks to his station wagon filled with reverence. At the Livingston Construction Company in North Fork, the gray-haired owner, Orville Livingston, reacts with incredulity upon discovering Homer is Black and declares he will never build the chapel. Homer, stung but defiant, insists he is doing the job and asks for two days of paid work a week. Livingston agrees, and Homer realizes he has committed himself without planning to.
A pattern forms. Homer lays the foundation and floor, works Thursdays and Fridays for Livingston, and spends his wages on groceries for the nuns. He puzzles over the surviving chimney that falls halfway down his chapel's right-hand aisle but decides against demolishing it. In late July, about 500 adobe bricks arrive from the community, and Homer begins laying walls. He runs out of bricks, and one moonlit night, listening to coyotes cry with a loneliness he understands instinctively, he drives to the city.
For two weeks he immerses himself in urban life, relishing the company of people like himself. When his money runs low, he takes a demolition job. Sorting salvage, he sees bathtubs and hears a compelling inner call, remembering the nuns hauling water from a well. He buys a tub and two small windows of red, yellow, and green diamond-patterned glass. A vision of his church returns, and he heads back.
The nuns greet his return as if he never left. He installs the bathtub, builds pews, and reflects on freedom: In the city no one commanded him, yet here, despite Mother Maria Marthe's bells and orders, he is free too, free like the lilies of the field, building his church because no one else can. Vehicles soon arrive bearing bricks from the Spanish-American community, each driver apologizing for doubting Homer. He resists outside help fiercely but gradually accepts assistance, especially from Juan Archuleta, a skilled adobe worker who helps set the windows into the walls. A Livingston truck delivers 1,000 high-quality bricks with no message. Homer builds the walls higher than planned, lays roof beams, and works with mounting urgency.
Mother Maria Marthe tells Homer that Father Gomez will say the first Mass in the chapel on Sunday, and Homer will sit in the front pew. His Baptist conscience recoils at sitting in the front pew of a Catholic Mass, but he cannot diminish her happiness. On Saturday he sits alone before his finished church. It stands strong against the blue sky, a crucifix at its peak. Inside, sunlight through the salvaged windows casts colored light onto whitewashed walls. He walks down the aisle, feels his throat tighten, and hurries out. Flights of birds head south. It is September, and his spring and summer are gone.
That evening the nuns sing with Homer's guitar. Later, he kneels alone in the dark chapel, trying to say something to God, but no words come. In the deep night he drives away, knowing he is never coming back.
The legend forms within hours. Newspapers run stories; tourists visit the chapel. Donations fund Mother Maria Marthe's vision: fine buildings, new nuns, and boys from troubled backgrounds studying and working. The chapel occupies the central position, its brick chimney rising above the flat roof like a steeple. Mother Maria Marthe, older now, guides visitors and directs attention to Sister Albertine's oil painting: a powerful Black man with his head thrown back in song, a nimbus of light around his head. She identifies the chapel as the Chapel of Saint Benedict the Moor and its builder as "a man named Schmidt who came to us under the direction of God. He built this chapel with his two hands under great difficulties. It is all from him" (118). She concludes: "He was not of our faith, nor of our skin, but he was a man of greatness, of an utter devotion" (127).