Codex — Lev Grossman

Edward Wozny, a hotshot young banker, is about to leave for vacation when he is sent to help an important yet mysterious client. His task: search the family library for a precious, centuries-old codex that may not even exist. Enlisting the expertise of medievalist Margaret Napier, Edward is determined to solve the mystery of the codex and to decipher the parallels between the codex legend and a computer game that absorbs him in the dark hours of the night.

Weaving the medieval and the modern aspects of its plot in a chilling twist, Codex is a thriller of the highest order.