They called it the killing day. Twelve people dead, all in the space of a few hours. Five murderers: neighbors, relatives, friends. All of them so normal. All of them seemingly harmless. All of them now dead by their own hand . . . except one. And that one has no answers to offer the shattered town. She doesn't even know why she killed—or whether she'll do it again.

Something is waking in the sleepy town of Oleander's, Kansas—something dark and hungry that lives in the flat earth and the open sky, in the vengeful hearts of upstanding citizens. As the town begins its descent into blood and madness, five survivors of the killing day are the only ones who can stop Oleander from destroying itself. Jule, the outsider at war with the world; West, the golden boy at war with himself; Daniel, desperate for a different life; Cass, who's not sure she deserves a life at all; and Ellie, who believes in sacrifice, fate, and in evil. Ellie, who always goes too far. They have nothing in common. They have nothing left to lose. And they have no way out. Which means they have no choice but to stand and fight, to face the darkness in their town—and in themselves.

It was like a nightmare, but there was no waking up. When the night began, Nora had two best friends and an embarrassingly storybook one true love. When it ended, she had nothing but blood on her hands and an echoing scream that stopped only when the tranquilizers pierced her veins and left her in the merciful dark.

But the next morning, it was all still true: Chris was dead. His girlfriend Adriane, Nora's best friend, was catatonic. And Max, Nora's sweet, smart, soft-spoken Prince Charming, was gone. He was also—according to the police, according to her parents, according to everyone—a murderer.

Desperate to prove his innocence, Nora follows the trail of blood, no matter where it leads. It ultimately brings her to the ancient streets of Prague, where she is drawn into a dark web of secret societies and shadowy conspirators, all driven by a mad desire to possess something that might not even exist. For buried in a centuries-old manuscript is the secret to ultimate knowledge and communion with the divine; it is said that he who controls the Lumen Dei controls the world. Unbeknownst to her, Nora now holds the crucial key to unlocking its secrets. Her night of blood is just one piece in a puzzle that spans continents and centuries. Solving it may be the only way she can save her own life.