One theme of the books is the exchange of bodies: those who know how to manipulate the power of the Gates may take the body of another, younger person to prolong their life, sometimes indefinitely through a series of such exchanges. This lust for immortality at the expense of others is seen at first as a kind of ultimate horror, but it emerges that there can be a contest of wills within the host body, one personality becoming dominant, but retaining the memories and skills of the others. The first three books form a trilogy linked by the pursuit of Morgaine’s ancient qhal betrayer Liell, who takes the body of Vanye’s cousin Chya Roh and flees from her via the Gates from world to world. Roh’s personality gradually subsumes the evil Liell; when Morgaine finally catches him, she spares him for both Roh and Vanye's sake. The fourth book is a sequel to the first three but in narrative terms is independent.