Halting State by Charles Stross
It was called in as a robbery at Hayek Associates, an online game company. So you can imagine Sergeant Sue Smith's mood as she watches the video footage of the heist being carried out by a band of orcs and a dragon, and realises that the robbery from an online game company is actually a robbery from an online game.
Just wonderful. Like she has nothing better to do. But online entertainment is big business, and when the bodies of real people start to show up, it's clear that this is anything but a game. For Sue, computer coding expert Jack Reed, and forensic accountant Elaine Barnaby, the walls between the actual and the virtual are about to come crashing down. There is something very dangerous and very real going on at Hayek Associates, and those involved are playing for keeps.
No cheats, no back doors, no extra lives - make a wrong call on this one and it's game over.