Set in the first century during the reign of the Roman Empire, the novel imagines the early life and spiritual journey of Lucanus, known to history as Saint Luke, the Greek physician who wrote the third Gospel of the New Testament. The story traces his path from a childhood marked by love and loss in Antioch, Syria, through decades of wandering the Mediterranean as a physician to the poor, to his arrival in Israel, where he gathers the testimonies that form his Gospel.
Lucanus grows up near Antioch in the household of Diodorus Cyrinus, a Roman tribune. His father, Aeneas, is a Greek freedman who serves as Diodorus' bookkeeper, and his mother, Iris, is a Greek freedwoman whom Diodorus has secretly loved since their shared childhood. Though Diodorus is married to the virtuous Aurelia, his silent devotion to Iris endures throughout his life.
As a boy, Lucanus feels a deep connection to the Unknown God, a deity honored in Greek tradition through a ritual wine libation, distinct from the capricious gods of the Roman and Greek pantheons. He prays to this God for the healing of Rubria, Diodorus' chronically ill young daughter and Lucanus' closest playmate. When the household physician Keptah uses Lucanus' gathered herbs and a luminous stone to bring Rubria relief, the grateful Diodorus pledges to educate Lucanus as a physician and grants Keptah his freedom.
Keptah, a Chaldean of mysterious origins educated at the university in Alexandria, becomes Lucanus' most important teacher. He instructs the boy in medicine and shares knowledge of an ancient priestly brotherhood called the Kalū, whose most sacred symbol is a golden cross representing a coming Redeemer. On the night of Jesus' birth, a brilliant Star appears in the heavens. Keptah recognizes it as the fulfillment of the ancient prophecy and worships in ecstasy, while the young Lucanus watches the Star move eastward until it vanishes at dawn. Keptah also takes Lucanus to a hidden Chaldean temple in Antioch, where the boy kneels before a great alabaster Cross and is overcome with adoration. Three Magi, actual Eastern kings, observe him and tell Keptah that God has special work for the boy, though he must first travel through long and arid places.
Keptah privately reveals that Rubria has the white sickness, an invariably fatal blood disease resembling leukemia. After a long remission, the disease returns, and Lucanus rebels violently against God. On a late summer afternoon, Rubria dies peacefully in her sleep while Lucanus sits beside her with his head on her knee. She has given him the golden cross that Keptah once entrusted to her. Rubria's death shatters Lucanus, and his bitterness hardens into a lifelong rage against the divine.
Other losses compound his grief. His father Aeneas drowns in a flash flood while trying to protect his account books. Aurelia dies giving birth to a premature son. Lucanus revives the apparently stillborn infant through mouth-to-mouth resuscitation, commanding the tiny body to live. The boy is named Priscus. Iris becomes the infant's guardian and eventually marries Diodorus.
Lucanus departs for Alexandria to study medicine, accompanied by his former tutor Cusa, now freed, and Cusa's wife Calliope. During four years at the university, he becomes a physician of extraordinary skill but remains spiritually bitter. His Jewish teacher, Joseph ben Gamliel, tells him of the Messiah prophecies and of a remarkable boy who astonished scholars in the Temple at Jerusalem, but Lucanus resists. He visits the dying Jewish merchant Elazar ben Solomon, whose infant son Arieh was kidnapped and is identifiable by a crooked little finger. Lucanus promises to search for the child. Elazar's daughter, Sara bas Elazar, comes to say farewell; Lucanus is drawn to her but refuses romantic attachment.
Before leaving Alexandria, Lucanus encounters Sira, a man with leprosy, fleeing through the streets. In a fury of compassion, Lucanus grasps Sira's shoulders and silently demands that God heal him. Sira is completely cured, though Lucanus does not witness the result. On the return voyage, Lucanus discovers plague among the galley slaves and, when the captain refuses to let him treat them, enlists a centurion and the reluctant Cusa to break into the galleys at midnight. Within three days, the stricken slaves recover. A letter from Iris brings news that Diodorus has died after delivering a defiant speech in the Roman Senate denouncing corruption. Tiberius Caesar himself honored the tribune with a funeral oration.
Returning to the family estate, Lucanus refuses an appointment as Chief Medical Officer, declaring he will travel the Mediterranean treating the destitute. Summoned by Tiberius, who respects him for Diodorus' sake, Lucanus serves briefly in the imperial household and receives a ring of imperial authority. At a banquet, the Empress Julia, Tiberius' dissolute wife, makes aggressive advances toward him. Lucanus rejects her violently, and the Praetorian captain Plotius helps him escape Rome in disguise.
For years Lucanus wanders the Empire's ports in spiritual emptiness. In Athens, he purchases and frees Ramus, an African king who cannot speak. Ramus comes from a hidden nation near Solomon's ancient mines and believes Lucanus will lead him to a deliverer for his people. The two become devoted companions. When a mob attacks Lucanus' house and slashes across Ramus' eyes, Lucanus expects irreparable blindness, but when the bandages are removed days later, the eyes are perfectly healed.
The centurion Antonius tells Lucanus aboard a ship how Jesus of Nazareth healed his dying servant from a distance simply by speaking a word. Lucanus dismisses the account but falls into a mysterious 14-day fever, during which vivid dreams call him to God. Ramus leaves the ship to seek Jesus in Israel. Sara, now terminally ill, writes a final letter telling Lucanus she has seen Jesus in Jerusalem; she dies at peace. Letters arrive from Ramus, restored to his people in Africa, describing how he witnessed Jesus raise a dead man and received back his own voice.
In Athens, Lucanus purchases a branded slave physician and, upon handing him a goblet, notices the crooked little finger on his left hand: This is Arieh ben Elazar, the lost child he has sought for 20 years. With Arieh, he encounters the wealthy young Jew Hilell ben Hamram, who is dying of spiritual despair after witnessing the crucifixion. Lucanus tells him Christ has risen, and Hilell is restored to health.
They sail toward Israel. On the road to Jerusalem, Lucanus raises a dead girl from her coffin, commanded by an inner voice. In Caesarea, he learns his brother Priscus is dying of stomach cancer. Priscus tells the full story of the crucifixion, which he supervised as a Roman officer: the procession to Golgotha, the supernatural darkness, the earthquake, and Christ's words from the cross. Lucanus prays fervently, and by morning the cancer has vanished completely.
Lucanus presents Tiberius' ring to Pontius Pilate, the Roman governor of Judea, persuading him to lift the proscription against Christians throughout the province. He visits the Apostles James and John and learns that Saul of Tarsus, a Pharisee who had been persecuting Christians, has seen the risen Christ on the road to Damascus and been transformed.
Traveling alone to Galilee and Nazareth, Lucanus gathers testimonies from those who knew Jesus. In Nazareth, he finds Mary, the Mother of Jesus, in a humble house. She appears at once eternally young and mysteriously aged, radiating a beauty and peace beyond the earthly. Mary tells him of the angel Gabriel's annunciation, her journey to her cousin Elizabeth, the Magnificat, her song of praise to God, the birth in Bethlehem, old Simeon's prophecy that a sword would pierce her soul, and her Son's quiet childhood. She describes a visionary encounter when Jesus was 14: a great dark angel appeared before Him on a hilltop, lifted crumbling earth to mock the world's worthlessness, and laughed; Jesus lifted the same earth, and it bloomed with lilies, and the angel fled.
At their final parting, Mary stands against the barren mounts clothed in light, lifting her hand in farewell and blessing. The novel ends here, directing the reader to the biblical Gospel of Luke and the Acts of the Apostles.