I usually try not to spoiler: in this case I shall do so wholeheartedly. Don't read on if it bothers you.
First I must comment on The Da Vinci Code phenomenon. Angels And Demons,(the movie) is a vague sequel (albeit the book precedes the Da Vinci book). While Da Vinci was hardly deathless prose, it told an interesting, unusual story at breakneck pace in an easy-to-follow manner. It was pacey and entertaining. It sold shedloads, and deservedly so. The movie adaptation was faithful, but lost the novel's immediacy: it still had broad appeal and did well at the box office, hence this sequel.
So to Angels And Demons (where I haven't read the book). In the run up to the Cardinals' voting in Conclave for a new Pope, four of them are kidnapped. Despite reservations about Robert Langdon (Tom Hanks, hardly pro-Catholicism in Da Vinci) the Vatican consults him. He figures out that this is the work of the Illuminati, a secret group dating back to the Renaissance, who seek revenge for the Vatican wiping out many of them in the 16th century for their pro-science, anti-Catholic views. Together with a lady scientist whose research generated an antimatter bomb stolen by the Illuminati, intended to wipe the Vatican off the map, Langdon engages in a clue-laden race against time, looking for the missing cardinals and the bomb. He is helped by Ewan MacGregor's Camerlengo Patrick McKenna (Camerlengo is acting Pope until the Conclave comes up with a new one - a functional rather than authoritarian position) and hindered by Stellan Skarsgard's head of Vatican police. Armin Mueller-Stahl is a Cardinal who may have his own agenda. There is further jeopardy from the fact that the Illuminati have probably infiltrated the Vatican at the highest level.
So far, so not-very-spoilery. Much action, racing around, convoluted clues etc., key factors which made Da Vinci so successful, albeit with a noticeably less credible plot. We even have have a couple of likely suspects - Starsgard's unhelpful police chief and Mueller-Stahl's cagey Cardinal.
Now for the rest of the plot. Three Cardinals are killed, but the fourth is saved. The bomb is recovered. However, there is insufficient time for it to be defused. McKenna takes it up in a news helicopter, and bails out. The bomb detonates, the shock wave causes relatively little damage, but McKenna's gesture in saving the Vatican and thousands of lives means he is certain to be voted in as Pope by popular acclaim. Of course, he turns out to be the villain, having murdered the old Pope and arranged the whole thing. Thank you, Robert Langdon, the end.
This pleased me in one respect - while the film still had you believing that the Illuminati existed, I wondered why they would leave a series of clues pointing to where the bomb was? Of course, as it was all McKenna's masterplan, he wanted the bomb found.
But then I started thinking about this masterplan. Let me list the parts of it (McKenna never does the standard explanatory monologue, you're left to figure it out yourself):
1. Steal antimatter;
2. Make antimatter bomb;
3. Poison Pope;
4. Recruit professional killer to kidnap and kill Cardinals;
5. Create trail based on incredibly complex clues from poem in priceless 16th century book in Vatican archive):
6. Rely on Langdon solving clues in time;
7. Make car bomb to blow up professional killer;
8. Rely on helicopter being nearby once bomb is recovered;
9. Rely on there being sufficient time to get helicopter, fly it high enough to avoid total destruction (despite nobody having the slightest idea exactly what effects of antimatter bomb might be), bail out, get to ground safely;
10. Rely on hero factor being sufficient to result in being elected as Pope.
The rationale (I think) was that, as Pope, he could prevent the Catholic Church living happily with science.
As a plan, I thought that this was risibly implausible. I happily suspend disbelief and willingly did so while the hunt was on, but the revelation of who the baddie was (and, therefore, what his plan must have been) was, to be frank, utterly idiotic - so idiotic, in fact, that it devalued the rest of the film.
There was some other stuff which made me scoff with derision:
McKenna is branded on the chest: a large glowing brand, maybe 20 cm square, is applied forcefully to his chest for upwards of 5 seconds, following which it is dropped to the floor where is sets the carpet smouldering. Yet this doesn't seem to phase him in the slightest - he races through tunnels and flies helicopters with nary a whimper (he does hold it as if it's a bit tender later on, though).
Earlier in the film McKenna tells a story about his military service which ends with him explaining that's where he learned to fly helicopters. It would have been a good deal less clumsy if he had simply whipped out a sign and hung it round his neck reading "I'm going to be flying a helicopter later in this movie."
Langdon rewinds the security video stored on the police chief's computer. The computer makes the noise of an audio tape being rewound across the replay heads!
My favourite bit was when the girl scientist tears a page out of a priceless 16th century book (the page which carries the all-important clues to finding the Cardinals and the bomb, in the form of a poem in English printed in watermarks in the paper!), not because it was an inherently good bit, but because I was immensely tickled at the gasp of horror coming from a lady in the audience.
This film was mistitled. It should have been called "Angels, Demons, And Complete And Utter B*ll*cks."