Natalie Greco loves being a law professor, even though she can't keep her students from cruising sex.com during class. She loves her family, too, but as a bookworm, doesn't quite fit in. Then, when a colleague talks Nat into teaching a class at a local prison, her comfortably imperfect world turns upside down.

A violent prison riot breaks out, and in the chaos, Nat rushes to help a grievously injured guard. Before he dies, he asks her to deliver a cryptic message: "Tell my wife it's under the floor."

The dying declaration plunges Nat into a nightmare. Suddenly, the girl who has always followed the letter of the law finds herself suspected of a brutal murder. Forced into hiding to stay alive, she sets out to save herself by deciphering the puzzle behind the dead guard's last words . . . and learns the secret behind the greatest puzzle of all—herself.