This is, I think, Terry Pratchett's best book.
Johnny Maxwell is sitting at his computer -- amazing what you can get when you say you need it for school work and your parents are going through Trying Times -- shooting away at the alien invading fleet when a message pops up on the screen: We want to talk.
He listens. He ends up taking their surrender. But it gets fun from there, because you know -- there isn't a button marked "Don't Fire."
All over, the game is no longer showing aliens, only an enormous starfield unless you leave it running for hours. Johnny has strange dreams where he protects their retreat to the Border -- and demonstrably communicates with someone else in the dreams. Meanwhile, times are still trying, the Iraq War is going on (Stormin' Norman and all) and Johnny has to help some friends. The interrelations between the alien plot line and the life as usual plot line are -- complex. With feedback.