Angels and Demons
In Angels and Demons a secret group is doing battle with the Catholic church.
At the start of the book a Physicist is murdered and a symbol has been burned into his skin.
The symbol belongs to the Illuminati. The group has a vendetta with the Catholic church and they plan to destroy Vatican City.
It's now up to Robert Langdon to solve an ancient mystery and save Vatican City.
But he has help. He meets up with an Italian physicist. This book has been made into a movie also.