Greg Bear's City at the End of Time starts simply enough, with people in modern-day Seattle. But they aren't normal people, and they have a connection with a future multiple trillions of years from now. In that future, the expansion of the universe has led to a weakening of the fabric of reality, and from that is born a non-reasoning entity called "The Typhon" that is destroying the laws of physics and eating reality.
But I've already misled you: the first chapter is in fact the very last. It doesn't make a lot of sense when you first read it because you don't have the context for it yet, but you'll come back to it at the end of the book and it'll make a bit more sense. Bear has constructed the book with multiple chapters out of order, so you jump about in time from the present day to the end of time and back, seeing the connections between the players and how the universe got to be in the mess it's in. Both the problem and the solution have to do with words, storytelling, and Mnemosyne (the Greek goddess of memory). And some of the stories within the story don't actually make any sense at all.
If it sounds confusing, it is. I didn't find it made much more sense after reading 500 pages, and I found those pages a brutal slog. It took me six months to get through this one - it's heavy going with a lot of ideas about how stories and words shape reality ... which, when I write it out, sounds good, but in practise was merely soporific.
About half way through I abandoned it long enough to re-read Bear's Blood Music - now that's a good book.