I think you should combine Scene 3 and Scene 4. Rather than having them be separate, the players are racing against time against the poison (which could be a sickness deliberately introduced into the well).
The epidemic by doing things like overwhelming the PCs and those they’re coordinating with the horror of the symptoms, like bleed-outs, agonizing deaths, whole households found contorted and stiff (Attack). Then seeming to abate, while it’s really incubating in record numbers of victims (Defense); suddenly a rash of infections turn up in the outlying areas of the settlement (Feint). Perhaps it gets into the food supplies, or even some of the medical supplies the players have been using (Maneuver).
If they do poorly, the epidemic wins. They may still figure out that it was poison, but the town has been decimated so badly that by next Spring it won’t even be a town.
If this is the first time you’re using Conflict, I’d be careful, though. It’s already somewhat abstract, and I wouldn’t rely on it being exciting the first time the group fumbles through the rules.