The Third Magic (ISBN 0-88899-126-6) is a fantasy novel written by Welwyn Wilton Katz and published by Groundwood Books in 1988.
Rigan is missioned to Earth to be reborn there and play a pivotal role in the constant war against the Line.
In the present Morgan Lefevre, who bears a striking resemblance to her ancestor Rigan, is pulled by the summoning into the world of Nwm, while visiting Tintagel as part of her father's TV show.
They attempt to cover up their failure and a power struggle results with Menw Power-Seeker killing the former Line leader, line-end Sdhe.
Part II While Rigan has been sent to Earth's past to influence King Arthur as he grows up, M'rlendd of the Line has also been sent there with similar goals.
She has a second vision showing the outcome of the task set before three other Sisters, sent to the north in search of a sword of power.
Arddu and Morgan continue to travel into the north, a dangerous land controlled by neither the Circle or the Line, but with both in pursuit.
They arrive in a land filled with intermixing symbols of both First and Second magic in which there stood a glass tower in a hill shaped like a hand surrounded by a lake.
They climb the tower and arrive in a room with a table on which lies a stone sheath for the sword, the Holy Grail and a severed, bleeding head.
Rigan is there with Mordred, and adds her First magic with M'rlendd's Second to allow Arthur to remove the sword from the stone.
She combines it with her half of the circlet, which she had received from her grandmother, having been passed down through the women of her family, and uses its power to wish for things to be the way they ought to be.
She realizes that one day she will take Arddu back with her to Nwm, where they will once again be free to live life as they choose, pretty coolly, away from predetermined destiny.