I love the continuing discussion. This chapter is in reply to the discussion in the comments. (I choose to use chapters for my plot planning most of the time. The rest of you can use either. Remember, though, that chapters will be easier to find later when you want to review an old idea.)
There are a lot of ways we can do this. Since we have two spy teams, the ones in court and the others in the field, then we could have two battles, the one described already with the fleeing city and the other one where the black powder is used. Two sets of spies allows information to be leaked no matter who is attacking first.
I suggest that the battles do not happen at the same time. In fact, one battle could be the result of the other one. Here's how: the North could test the powder in the field, and the second battle is in retaliation for the use of the powder.
I would guess that the first battle is when we introduce the Luke/Lewis angle that we have discussed previously. Perhaps, as discussed before, the South is either unaware of the powder or only has a vague idea, and the spy network is still secret. The retaliation could be after the spy network is discovered by the South. The retaliation is successful because of their newly discovered spies. When the South retaliates, that's when people flee the city, nearing the end of Masquerade.
The other events about the North discovering the spy network can happen in between the two battles, so when the second battle is taking place, that's when the kidnapping/capture would take place, and that's also when Jon's fake death would happen.
The more we discuss this, the more the timing of events is coming together for me. Perhaps I will post the timeline idea suggested in the comments. We could each post our version of it and decide on a final version to go by for the rest of the story.