@Dafydd - Are any objectives unchecked, besides "Don't kill Basso"?
@Bobber - You need to get into Stonemarket to continue the mission. Have you noticed the keypad by the power station area? How about the City Watch storage with the red lock? There's also a alcove near the Stonemarket gate you might want to check out.
@Cardia - nickie is right - you need the code to overload the system. Check out the document on the wall in an area above the keypad. Once you read that, find the four coils spread throughout Southquarter and then make your calculations.