The Maid of the White Hands: The Second of the Tristan and Isolde Novels

Isolde's day has come. In Ireland her mother, the Queen, lies dying. The throne of the Emerald Isle, one of the last strongholds of the Goddess, awaits her. But while Ireland is her destiny, Isolde is already Queen of Cornwall, trapped in a loveless marriage to the mean-spirited King Mark. Her true love is his nephew, Tristan of Lyonesse, who has never married, remaining faithful to Isolde.
Across the sea in France, a young princess who shares Isolde's name enters the story. King Hoel named his daughter in honor of Isolde of Ireland, but young Isolde of France has always been determined to outdo Queen Isolde. She, too, is a physician and is called "Blanche Mains," for her white hands and healing touch. Blanche is of an age to be married, and she has chosen her husband--Tristan of Lyonesse. Her father objects, but fate favors Blanche. King Mark has become suspicious of his wife and nephew, and when Tristan is wounded in battle, he sees a chance to separate them for good.
Mark sends Tristan to France to be healed by Blanche, who makes the most of the opportunity. Tristan's letters to Isolde are intercepted, and he is told that she has given him up. Near death from his wounds, Tristan sends one last desperate letter to Isolde by a trusted servant. He is dying, he tells her, and asks for one final sign of their love. If she can forgive him for marrying another, she must come to France in a ship set with white sails. If the ship's sails are black, he will know that she no longer loves him. Isolde immediately leaves for France, but when Blanche sees the white sails from the castle window, she pulls the curtains and tells Tristan that they are black. To her horror, he turns his face tothe wall and dies.
There ends the traditional medieval story of Tristan and Isolde--with betrayal, death, and grief. But the original Irish legend ends differently, and so does this book, with magic and drama as only Rosalind Miles can write it.