Angels and Demons   by Dan Brown

This is Dan Brown's best. People opposed to the Vatican have taken antimatter from CERN and hidden it in Vatican city, where it will annihilate in a few hours, taking all of Vatican city with it. The pope has recently died (turns out he was murdered), and conclave is in progress, so that all the world's cardinals are present in the Cistine Chapel. The terrorists have wrapped the plot up to make it look like the resurgence of an ancient sect of scientists (Illuminati) with a vendetta against the church, and ancient mysteries are re-enacted (path to illumination) which provide cryptic clues to the perpetrators.

Thus a professor from Harvard finds himself following a trail of killings across the churches of the city of Rome, trying constantly to get ahead of the killer and thus prevent the atrocity from happening. In the process, he puts his own life in danger.

This is as good as I can imagine action-adventure ever getting.