
Born of a Saxon woman named Erce, Derfel and his mother were once captured in a raid by Britons and enslaved. The narrator, Derfel, is a young foundling at Ynys Wydryn who had been adopted by Merlin. Merlin himself has not been seen in Britain for many months.

The infant Mordred and his mother are brought to Merlin's hall at Ynys Wydryn, where she and the child are placed under the care of Merlin's priestesses, Morgan (Arthur's sister) and Nimue (Merlin's lover). The High King dismisses the sign and declares that the son will be named after his father: Mordred. The pagan magic seems to work and a male child is born, but with a crippled leg, which is seen as a very bad omen. Uther, a pagan, finally loses patience with Norwenna's Christian midwives and summons Merlin's priestess Morgan to deliver the child. Queen Norwenna is in labor, and there are fears that she and the child may die. Dumnonia's only hope is for Mordred's pregnant wife, Norwenna, to give birth to a son. High King Uther Pendragon blames his son's death on Arthur and exiles him to Armorica.

Its forces, led by the Edling (crown prince) Mordred and Arthur (the king's bastard) have defeated the Saxons at a battle beneath White Horse Hill, but at a terrible price: Prince Mordred was slain, leaving the kingdom without an heir. Most of the narrative is recounted in a series of flashbacks to his life as a young man, with regular intermissions in the present-day monastery. Knowing that his unsympathetic master Bishop Sansum cannot read, Derfel pretends to write a Christian gospel. In the monastery at Dinnewrac, the young Queen Igraine begs Derfel to record his tales of how he met the many famous heroes of Arthurian legend. The story is narrated by its main protagonist, Derfel Cadarn, an elderly monk who has converted to Christianity late in life after spending many years as a warrior in the service of Arthur, a renowned warlord who long ago fought to protect the kingdom of Dumnonia. However, on the cusp of a united peaceful Britain, Arthur's decision to marry Guinevere plunges the island into war again. After being banished to Armorica by his father, the High King Uther Pendragon, Arthur returns to protect the new king, his infant nephew Mordred.

A former warrior sworn to Arthur and now an elderly monk, Derfel tells the story of how Arthur became a warlord in Dark Age Britain despite illegitimacy to the throne.

The novel is divided into five parts narrated by the protagonist, Derfel Cadarn. The book is based on characters and plot elements from Arthurian myth, but considerably changed and re-worked. The Winter King: A Novel of Arthur is the first novel of the Warlord Chronicles trilogy by Bernard Cornwell, originally published in the UK in 1995 by Penguin Group.
