The Illuminati are out for revenge against the Catholic church, and there's only one man who can stop them: whoever the Tom Hanks character is! In Angels & Demons, Hanks uses the same skill set he used to decipher the Da Vinci Code (thought, sometimes running) to foil the enemies and learn something about Christian lore that your mom will mistake as fact.
From the looks of the trailer, they've added some underwater parts to make the video game better:
Girls looking for their dolls are better than bloodhounds when searching for corpses. That's what I learned. How about you?