Brandon Sanderson
The City Guard Attacks
Some of you may be wondering whose plot led to this attack by the city guard on the meeting.
Well, it's complicated. The city watch—worried about the upswing in crime and the political tension lately—has grown more aggressive. They know that someone snuck into the palace of Mercystar herself, threatening one of their goddesses. The watch captain is making a play for a promotion and favor, and is looking to score a major victory to look very good in front of the Returned. He got a tip that three of the most important slumlords—whom he's been afraid to attack up until now, fearing to commit his guards to action—will be meeting together. He doesn't even know about Vivenna.
But he did authorize his Lifeless (the city guard has a stock of about fifty that can be used at their discretion) to use deadly force. The Commands weren't quite specific enough, unfortunately.
Beyond that, Bluefingers has managed—by sneaking through the tunnels that Vasher discovered—to get his forces to Command Break some of the Lifeless in the compound, then insert hidden Commands into them alongside their existing ones. In this case, he wanted the Idrians to see the Lifeless and the city watch cause a slaughter among their people. So he seeded some of the Lifeless with Commands to attack and kill if they were shown aggression by Idrians.
He didn't know when the slaughter would happen; he doesn't have enough control over events in order to do that. His little Lifeless bombs just happened to go off here, when the Idrians started to resist. Since the regular soldiers—and even the Lifeless not under Bluefingers's Commands—overreacted once blood began to be shed, everything went crazy from there.
Denth wasn't in on this plan, and Bluefingers never told him that he was behind it. In the end, the whole battle turned into a major embarrassment for the city guard, though they did capture one of the slumlords. He was held until after the events of the book, then eventually released.