Thea has a secret. She can tell how long someone has left to live just by touching them. Not only that, but she can transfer life from one person to another—something she finds out the hard way when her best friend, Ruth, suffers a fatal head injury on a night out. Desperate to save her, Thea accidentally kills the man responsible and lets his life flow directly into Ruth.

Thea comes to understand that she has a godlike power, but how to use it quickly becomes a question of self-control. Is it really so wrong to take a little life from a bad person—say, a very annoying boss—and gift it to someone who's truly good? Realizing she needs to harness her newfound skills, Thea creates an Ethical Guide to Murder. But as she embarks on her mission to punish the wicked and give the deserving more time, she finds good and bad aren't as simple as she first thought.

How can she really know who deserves to live and die, and can she figure out her own rules before Ruth’s borrowed time runs out?