Omega

Jack McDevitt has a really interesting science fiction book here. Set a couple of hundred years in the future, with humans possessing faster-than-light travel, and all sorts of other nifty technological doodads, the story is of the "Omegas", big ol' scary interstellar travelling clouds that, well, home in on and destroy whatever looks like civilization - e.g., right angly stuff. Humans are looking for neighbours in the universe, and have found a couple - a bunch that like to fight, and a bunch that got walloped by the Omegas and went from some pinnacle of evolution to clubbing things with sticks.

Humans find another civilization because one of the clouds they're tracking noticed it and wandered over to beat up on it. Humans are also scared 'cos one of these clouds is coming to pay a visit in a few thousand years. Humans also know that they can't do much with these clouds - for example, they're not terribly bothered by a bunch of nuclear explosions inside them. Humans figure that this could be a good test run to fend off a cloud; besides, maybe they can make friends with the really nice civilization they found.

Fairly standard sci-fi stuff. What makes the book interesting (and I suspect it is contingent on the reader actually responding to these themes) is the way the story includes trenchant observations on ego, faith, epistemology, doctrine, and humanity.

I think I'm going to hunt down his "Polaris" and "Chindi".