Surface Detail by Ian M Banks

With virtual realities offering a form of immortality to the races of the galaxy some groups are not satisfied with ever lasting paradise for all. They have created virtual hells in order to keep people on the straight and narrow for fear of eternal punishment. Their neighbours are so upset by this cruelty that war has broken out. The Culture gets involved in its own bumbling way with the help of an escaped slave girl.

Another great read set in Banks' Culture universe.