After his twin's accidental death, twenty-one-year-old Will Creed commits suicide in an attempt to escape his pain, but instead finds himself wide awake in the Afterlife, where he discovers that, unlike him, his brother was sent to Hell. Desperate to rescue his brother, no matter what it takes, Will follows a god to Hell, where he meets Lucifer, who has lost patience with humanity and intends to extinguish all life on Earth.

Torn between the need to save both his brother and mankind, Will travels back and forth between the worlds, where he gradually uncovers the Devil's darkest secrets and falls in love with the last person he ever expected.