The Imperium Game (Del Rey Discoveries)

The Game was authentic from top to bottom, and most players had forgotten it was a game. When the reigning Emperor really was murdered, the prime suspect was the game's main programmer, Kerickson. Fired from his job, pursued by a policeman convinced of his guilt, Kerickson sneaked into the Game to find the real murderer. But he had lost access to his control room and only had the aid of the mouse-munching owl who was the Goddess of Wisdom--if only she were programmed correctly. But Minerva had more bugs than Cerberus had teeth.