An ancient secret brotherhood.
A devastating new weapon of destruction.
An unthinkable target.

World-renowned Harvard symbologist Robert Langdon is summoned to a Swiss research facility to analyze a cryptic symbol seared into the chest of a murdered physicist. What he discovers is unimaginable: a deadly vendetta against the Catholic Church by a centuries-old underground organization -- the Illuminati. Desperate to save the Vatican from a powerful time bomb, Langdon joins forces in Rome with the beautiful and mysterious scientist Vittoria Vetra. Together they embark on a frantic hunt through sealed crypts, dangerous catacombs, deserted cathedrals, and the most secretive vault on earth...the long-forgotten Illuminati lair.

SPOILER: sent in by Dallas E.

In this prequel to The Da Vinci Code, Robert Langdon teams up with Vittoria Petra, the adopted Daughter of a murdered Physicist/Priest to track down the whereabouts of a stolen piece of new technology, Antimatter.  The thief has stolen a sample and hidden it within the walls of Vatican City on the eve of a Conclave being held to elect a new Pope.  The sample has a destructive capacity exponentially greater than dynamite and could level Vatican City if it explodes before Langdon and Petra can find it.

Also in the mix is the motive for the situation, Revenge, from an ancient brotherhood who has come back to defeat Catholicism once and for all, The Illuminati.  Langdon follows a path known as the "Path of Illumination" to try and locate the person responsible for the "bomb". 

Langdon is aided in his quest by the former "right hand man" to the Former Pope Carlo Ventresca, who, as it becomes clear, is the actual murderer of the Pope because Ventresca thinks that the Former Pope was a sinner.  Ventresca has set the whole situation up so as to eventually come to the rescue and "find" the bomb, which he would then dispose of and get the college of Cardinals to believe that God told him where the bomb was so as to get elected himself and set a new , higher, standard for the office of the Pope.

Langdon saves the day and Ventresca is found out and kills himself.