Andy and the Old Guard face Cassius Draken, a vengeful foe with a weapon to destroy immortals. Lysandra, thought lost, returns with secrets that force the team to confront betrayal and their fragile existence.

Andy and her team of immortal warriors continue their mission to protect humanity. This time, they have to face off against a formidable new foe who threatens the very fabric of the Old Guard, while also dealing with the return of an immortal who was thought to be long lost.