Please boost if you’re still masking indoors (in public places)

I ran into a wall writing an adventure arc. So far the party have retrieved a maguffin for a local lord, escorted a messenger for that lord to a political summit going bad. And now I don't know what I want to do for the final act. I was thinking of including a doppelganger trying to start a war, but I can't think of a set piece that will fit in a 2-3 hour slot. #ttrpg #adventure

I am about to test side based initiative for my new game. Does anyone have experience with it, or know of any stumbling blocks?