Orphaned during an Irish raid, Tristan (James Franco) is raised by his uncle, Lord Marke of Cornwall (Rufus Sewell), who tries to unite the British tribes against their would-be Irish conquerors. Wounded during battle, Tristan is believed dead and set adrift on a burning bier. He washes up in Ireland, where he's nursed by the daughter of King Donnchadh (David Patrick O'Hara), the rambunctious Isolde (Sophia Myles). She keeps her own identity secret as they fall in love. When Tristan’s compatriots come hunting for him, she sends him off with a kiss and lament that "This cannot be." But as soon as Tristan returns home, Donnchadh decides to give away his daughter to the winner of a contest among the British tribesmen, hoping to divide them in the process. When Tristan wins her for Marke, she's horrified to learn her husband is not Tristan, just as he's horrified to learn she is the princess. After the marriage, Tristan dissolves in depression, until they begin to tryst in secret.