The series is based on the unpublished young adult novel of the same name by Frank Miller and Tom Wheeler, and tells the legend of King Arthur from the perspective of Nimue, who is destined to become the powerful but tragic Lady of the Lake. The story tells that after Nimue's mother passed away, she unexpectedly became a partner with the young mercenary Arthur, and they will work together to find Merlin and hand over an ancient sword. During the journey, Nimue will become a symbol of the fight against King Uther and the Red Knights.