Machika Balfaltin inherits her late grandfather's unfinished bounty: kill the immortal known as Methuselah. When she finally tracks him down, she finds Rain Jewlitt, a clumsy, gentle man who has lived for centuries and lost more than he can carry. Unable to bring herself to take his life, Machika tags along as Rain waits for Yuca, the figure tied to his immortality, while bounty hunters and a shadowy organization close in around them.