Set against European colonialism in Morocco and the devastation of World War I, the novel follows a Berber boy, a magnificent Arabian mare, and the people whose lives they touch across two continents, all linked by the scattered beads of an amber necklace.
In 1899, in Morocco's High Atlas Mountains, a Berber woman named Aisha gives birth to her son Beddou. He grows into a clever, restless boy who memorizes Koranic verses easily but cannot sit still in school. His father, Abdellah, sends six-year-old Beddou to work as an indentured shepherd for a cruel distant cousin named Saïd. Before the boy departs, Aisha hides a necklace of six amber beads on a red silk cord inside his cape, telling him the beads will keep him warm and bring him home. Saïd sends the boy to tend sheep alone in the mountains for years, and when Beddou's father dies, Saïd traps him as an unpaid servant. Beddou's only comfort is Louhou, Saïd's kind young wife.
Meanwhile, in the Sultan's palace in Fes, head groom Omar's finest broodmare delivers a perfect filly, though Omar's own infant daughter is stillborn the same night. He names the filly Aziza. Years later, the mare is given away as a royal gift and passes through several owners before reaching the garrison at Meknes.
Around age eleven, Beddou is rescued by Hassan, a stranger who stages the boy's drowning, pockets one amber bead as payment, and carries him to Meknes on horseback. Beddou is apprenticed to the saddlemaker Haj Ali, learns Arabic, and becomes skilled with horses. He reunites with Louhou, who has fled Saïd and now works as a
shikha, a singer and dancer, and gives her an amber bead. When an emissary tries to beat a panicking mare at the shop, Beddou calms her. Hassan swaps the valuable mare for an inferior one and gives her to Beddou, who names her Tassa, meaning "beloved."
Jean-Baptiste Thibault, a massive French colonial soldier born in Algeria, is also stationed in Meknes. A gifted card counter, he exploits Hassan's vanity until Hassan gambles away both Tassa and Beddou's indenture contract. Hassan and Beddou attempt to steal back the mare, but Beddou is caught while Hassan escapes with the horse and never returns. Hassan enlists in the French Colonial Army and is shipped to France with Tassa in August 1914, carrying two amber beads: one from Beddou and one from Louhou.
In Northeast France, Tassa marches with Hassan's Spahi regiment, a Moroccan cavalry unit in the French Army, into the Ardennes Forest, where they walk into German artillery. Tassa bolts at the first blast and gallops to a meadow near a yellow house with blue shutters. There, Estelle Maillot, a young Frenchwoman, lives alone with her physically disabled brother Léo, who cannot walk independently. Estelle coaxes the terrified horse into her stable. Thomas Bellows, an English veterinarian volunteering with the Blue Cross, a humanitarian horse-care organization, runs a makeshift hospital nearby. Haunted by his sister's death and his own addiction to morphine, he visits Estelle and helps free the mare when she becomes stuck in her stall. Hassan reappears, reunites with his horse, and asks Estelle to post a letter to Beddou confessing that he stole Tassa. He departs with the mare, warning that German soldiers fill the woods.
When a German officer threatens Léo, Estelle grabs her father's hidden rifle and shoots the officer. Hassan helps conceal the body and rides off. Before dawn, German soldiers retaliate by seizing Léo and burning Estelle's house. In town, they line up civilian captives, including Léo, before a firing squad. Jean-Baptiste, who lost his memory in an artillery blast and now wears a dead German soldier's uniform, has been swept into the group. He is about to fire when Hassan charges through on Tassa, scattering the soldiers. Seven civilians die, but many escape. Jean-Baptiste is captured and sent to a prisoner-of-war camp in Morocco.
In the aftermath, Hassan gives Thomas an amber bead for safekeeping. Thomas finds Estelle alive near her ruined house. She joins his veterinary hospital, and they develop a deep bond, sharing their secrets and a first kiss. When Estelle slips through German lines to search for Léo at a nearby Abbey, she does not find him. The nuns disguise her as a nurse, trapping her in occupied territory for the rest of the war.
In Meknes, Beddou receives Hassan's letter, read aloud by a scribe. Jean-Baptiste, having escaped the prisoner-of-war camp, arrives at the saddle shop with the indenture contract, claiming ownership of Beddou. Beddou leads him to Louhou, who extracts and burns the contract stick, freeing Beddou. Louhou reveals she originally sent Hassan to rescue Beddou years ago. Jean-Baptiste learns Hassan and Tassa are in France and returns there, establishing himself as a horsemeat butcher in occupied Courte-Chapelle.
In 1916, the mare arrives at Thomas's hospital among wounded horses, filthy and dispirited. He names her Mystery. In early 1917, Estelle receives a grievously wounded soldier at the Abbey: Most of his face is burned, one arm is amputated, and he carries an amber bead and an unfinished letter in Arabic. She whispers "Hassan?" but receives no recognition. She calls him
le capitaine and cares for him until he dies of influenza in October 1918, weeks before the Armistice. Estelle takes his bead and accepts a position at a school for children with disabilities in Paris.
Beddou receives Hassan's unfinished letter, forwarded by Estelle, and trades his second-to-last amber bead for passage to France. After months of travel, he collapses near the Abbey. Thomas, returning to Courte-Chapelle with the mare after the war, finds Beddou on the road and carries him to the nuns. Beddou later escapes and encounters Thomas and Tassa in the woods. Thomas nearly shoots the boy before the mare intervenes, going to Beddou the moment he whistles three familiar tones.
The Abbess urges Estelle to accept a marriage proposal for her protection, as neighbors blame her for the wartime massacre. Estelle assumes the suitor is Thomas but finds Jean-Baptiste. She flees to the old veterinary stable, where she reunites with Thomas. Jean-Baptiste arrives with a policeman, claiming the mare with a forged pedigree. Beddou pretends to read the Arabic script and recites a Koranic verse about war horses that he memorized as a child. Thomas produces a page from Shakespeare's sonnets as a fake marriage certificate. The bewildered policeman arrests Jean-Baptiste.
In the stable, three amber beads are brought together:
le capitaine's bead from Estelle, Hassan's bead kept by Thomas, and Beddou's remaining bead. They piece together Hassan's story, realizing he charged the firing squad, saved Léo, and tied an amber bead around the boy's neck before entrusting him to Belgian refugees. Thomas asks Estelle to leave with him, but she insists on searching for Léo. They depart together in the horse ambulance with Beddou and Tassa.
Beddou returns to Morocco, delivers news of Hassan's death and his
Croix de Guerre, a French medal of valor, to Louhou, and rides Tassa home to his mother Aisha, who is alive and remarried. The epilogue reveals that Beddou emigrates to America under the name Thomas Bellows, raises Arabian horses in Wyoming, and dies at approximately 98, his amber bead passed to his granddaughter. Thomas and Estelle open a café in Morocco called Chez Estelle. In 1924, Estelle receives a letter from a school in Sussex, England, confirming that Léo was brought there by Belgian refugees in 1914, wearing an amber bead. He lived happily before dying of Spanish flu in 1919. The novel's final document records Hassan's death and his official classification: "Fallen for France."