Set in sixth-century Britain during the decades following the collapse of Roman rule, the story follows Owain, a 14-year-old boy of Roman-British descent, through years of loss, bondage, and gradual renewal as Saxon kingdoms consolidate power over the former Roman province.
Owain regains consciousness among the dead on a battlefield near Aquae Sulis (modern Bath), where the last British forces under Prince Kyndylan the Fair have been destroyed by Ceawlin, Lord of the West Saxons. He finds his father and older brother Ossian among the fallen and takes the family's ancient signet ring, bearing a dolphin carved into a flawed emerald. He bonds with Dog, a young brindled war-hound from Kyndylan's pack, and the two flee north.
Resolving to reach Viroconium (modern Wroxeter) in hopes that survivors may regroup there, Owain collapses at a small hill farm. Priscilla and her husband Priscus, a former master potter, nurse him through weeks of fever. Priscilla offers him a son's place, but Owain refuses. He reaches Viroconium on a rainy autumn day and finds the city gutted and deserted. In a ruined shop he breaks down, accepting that his world is gone.
That evening, cooking a hare in Kyndylan's Palace, Owain encounters Regina, a girl of about 12 with extraordinary grey eyes, drawn by the smell of meat. She lived with an old woman who forced her to beg; when the woman died, Regina stayed alone in the ruins because the city is the only place she knows. They begin sharing a lair. When a blue tit flies into their shelter, Regina catches it, shows it to Owain, and releases it, a moment of shared delight that becomes significant later.
Through a hard winter they survive on hunting and dwindling grain. British outlaws raiding cattle occupy the Forum and capture Regina. Owain stampedes the cattle with sling-stones and she escapes. They hide beneath the floor of a ruined house, where Regina's hand touches a skeleton, the remains of an old man who once threw her a copper coin. The discovery makes Viroconium unbearable. They decide to steal a boat on the southeastern coast and cross to Gaul.
Traveling southeast, Regina develops a severe lung illness. Owain buries his father's ring under a great thorn tree and carries her to a nearby Saxon farm. A young Saxon named Beornwulf offers to buy Owain as a thrall, a bonded laborer, for a gold piece if the household cares for Regina. Owain accepts, knowing there is no other way to save her.
More than a year later, Owain lives at Beornstead, Beornwulf's farm on a coastal peninsula in the South Saxon kingdom. Uncle Widreth, an elderly half-British relative in the household, tells Owain that while one is young there is always hope "that one day a little wind will rise" (112). Owain overhears Beornwulf and his foster brother Haegel, King of the South Saxons, discussing Ceawlin's growing power.
Two years later, Owain delivers a silver-white foal from Beornwulf's mare on the land of Vadir Cedricson, a powerful and cruel neighboring lord. Named Teitri, the foal will grow pure white and be sacred to the god Frey, eventually sacrificed. Over the following winter, Owain partially breaks Teitri in a struggle that ends not in mastery but in the horse freely giving his trust.
Grief accumulates. Uncle Widreth and the youngest child die. Teitri is sent away as a royal gift. Vadir's hounds attack the aging Dog and kill him. Owain mercy-kills Dog while Vadir watches unmoved and taunts Owain, implying he fled Aquae Sulis. Owain buries Dog at a ruined shrine in the oakwoods. Alone there, drifting toward ending his own life, he notices sunlight on a blue glass tessera, a small mosaic tile, in the floor and uncovers a mosaic of a girl holding a bird. The image triggers a vivid memory of Regina with the blue tit. Owain becomes certain she is alive and finds a reason to go on.
Beornwulf's ship wrecks in a gale, and Owain rescues him from the surf. Beornwulf offers freedom, but Owain asks to delay removal of his thrall-ring, the iron band marking his slave status, until the King's war-summons comes, requesting a sword to fight Ceawlin. When the summons arrives, he has the ring cut off and claims a blade.
The Saxon alliance, joined by treaty with the British kingdoms, marches against Ceawlin. A British envoy named Einon Hên, a fierce one-eyed old nobleman, calls the bond between Owain and his Saxon comrades "The Truce of the Spear" (190). Because Owain speaks British, he carries the battle plan to Prince Gerontius of Powys, the British commander. At the British camp he sees the Red Dragon standard flying again but refuses Gerontius's invitation to stay, honoring his oath. The Battle of Wodensbeorg is won and Ceawlin flees, but Beornwulf is mortally wounded. Dying, he asks Owain to stay at Beornstead until his son Bryni turns 15. Owain promises.
Owain manages the farm through years of harvest and lambing. At the wedding feast of Beornwulf's eldest daughter Helga, Vadir sweeps another daughter, Lilla, into the bride-race, a horseback contest among wedding guests, and three days later comes to ask for Lilla's hand. The terrified girl runs to Owain, who offers to remain beyond his promised time if Beornwulf's widow Athelis will delay Vadir for a year. His freedom is postponed again. Meanwhile, Bryni wins Haegel's attention by killing a wild boar.
Haegel brings Bryni and Owain to a Council at Cantisburg (Canterbury) convened by Aethelbert, King of Kent. There Owain reunites with Einon Hên and witnesses a historic event: a party of Christian monks from Rome, led by Augustine, lands on the Kentish coast. Aethelbert meets Augustine outdoors, fearing indoor enchantment, and grants the monks permission to settle and preach. Einon Hên reflects that even the political maneuvering behind this moment might hold something wonderful: "Not the dawn as yet, Owain, but I think the dawn wind stirring" (269).
A drunken quarrel erupts between Bryni and Vadir over Lilla. They draw lots in an old custom, and Vadir draws the longer grass-stem, marking him as the loser who must face a mortal hazard before sunrise. He chooses to ride Frey's Horse, the sacred unbroken white stallion. Teitri hurls himself toward a thorn tree and Vadir's neck is broken. Owain flings himself between the maddened horse and Vadir's body, calling Teitri's foal-name until the stallion calms. With Vadir's death, Lilla is free, and so at last is Owain.
After the harvest, Owain takes his leave, gently refusing Lilla's plea to stay and advising her toward Horn, Brand the Smith's son and her intended match. He travels to the farm where he left Regina 11 years ago and learns she fled after the farmer tried to claim her. At the thorn tree, the ring is gone; in its place he finds a sealed pot containing a lock of black hair tied with scarlet thread, Regina's sign that she took the ring and wants him to follow.
He reaches Viroconium in autumn. The ruins are softened under willow-herb. Regina stands at the old grotto with a water-crock. "I knew that you would come one day" (296). She returns his father's ring; it fits now. Owain tells her they will not go to Gaul: "That was for the dark; now, there's a dawn wind stirring" (299). They will go southwest to the hill farm of Priscilla and Priscus, and if the old couple are gone, build a life there themselves. Together they walk toward Kyndylan's Palace to share a meal and begin again.