Angels and Demons by Brown Dan

When a CERN scientist is found murdered, the investigators decide to contact Robert Langdon for assistance. A Professor of Symbology at Harvard, Langdon can't understand why the police need his help. When he arrives, he discovers a series of strange symbols which link the murder to the Vatican, where the College of Cardinals has assembled for one purpose: the election of the new Pope. The entire world is watching as the ballot boxes are collected, but unless Langdon can help solve the clues in time, a deadly bomb waits beneath the city, waiting to go off.