This time around I figured I'd review the novel before I even have read the book. Please note I haven't read the book and I don't have an advanced copy of the book. Instead I'm basing my review completely on what I've read in the previous books. I figure I can get about 85% correct so if this spoils the novel for you then I'm sorry.
The book opens in Florence Italy where an old man is being chased. He's able to avoid his pursuers long enough to hide some crucial piece of information that will become important later even though it seems silly now. The old man is now murdered and we immediately cut to...
Robert Langdon being awoken. The author is just trying to show how clever he is as he understands time zones. Langdon soon learns that an important figure in the symbolism sect has been killed and only Robert Langdon can help solve the problem. He then gets off to Florence Italy.
Where he's taken to the crime scene where he meets the Misguided Policeman who immediately starts off on a bunch of exposition to catch up all us readers on why this person is important. Then the love interested walks in and we soon discover that she is the daughter/grand-daughter/adopted daughter of the dead man. The Misguided Policeman gets a phone call/interrupted by underling and leaves the two alone to talk where Langdon realizes that this is all a big puzzle related to Dante's Inferno.
At that point Misguided Policeman realizes that Langdon must be in on it somehow even though he was an ocean away when the murder was committed. The chase is on! Langdon uses his knowledge of medieval Florence to give the police a slip. Not realizing that they are being chased by a crazed assassin who has a some sort of glaring physical trait like a unicorn horn that should make him easily spottable from space.
Langdon and love interest run around Florence solving clues only to get to a point where they need help. Langdon now realizes he knows someone near Florence that can help so they go to them for help. Super Spoiler Alert! This person they go to for help is the villain who is pulling all the strings from behind the scenes.
Now the three of them are running around Florence solving clues and heading towards a final conflict where Langdon realizes that the help is the villain and tricks him into thinking that he can't solve the final puzzle. The Misguided Policeman finally realizes who the true villain is and arrests the help and guns down the crazed assassin.
Langdon and the love interest go off and solve the final puzzle and for some reason even though beautiful women keep throwing themselves at him Langdon once again fails to seal the deal.
Well that's my best guess. Feel free to leave a comment to let me know how right or wrong I am.