After the fall of Rome, visionary warlord Marke (Rufus Sewell) seeks to unite the squabbling English tribes to form one strong nation and defeat the brutal Irish King Donnchadh. But when Lord Marke's greatest and most loyal knight, Tristan (James Franco), falls in love with Isolde (Sophia Myles), a beautiful Irish woman, it threatens to destroy the fragile truce and ignite a war.