Angels and Demons – the novel, not the movie. I started it, but gave up after a hundred pages.
It seemed extremely unrealistic to me that somebody with an actual college degree, a Harvard professor no less, had never even heard of anti-matter. The grade-school level explanation of this and related technologies, to Robert Langdon, college professor, annoyed me. Most colleges require at least basic physics and chemistry for almost any degree. Although the author must present that material in some way, he should have found a way to do it that fit; maybe by having the scientist explaining it to a college freshman, or a reporter.
Having said all that, the science itself was plausible. However, nobody has made anywhere near the quantity of anti-matter described. The novel did cover that aspect, though, with a reasonable fictional explanation. I did have a bit of a problem with the idea that an extremely intelligent top physicist would allow that much anti-matter to be stored in a container requiring electrical power to sustain it, considering the consequences. Such a scheme would be criminally irresponsible in the real world. By comparison, nuclear bombs are very safe – you have to set them off. With this thing, all that has to happen is an interruption in the electrical supply.
The book is probably a pretty good read for some people, but I just lost interest because the factors above.