As written: tell them that they crest a hill and see to the east that smoke is rising from the town and that a huge winged form passes overhead. Thunderclouds gather and whirl above. Lightning strikes. Does the party leave or engage?
Leave: commence hexcrawl procedures (product not included—yet)
Engage: commence the raid turn
Modified: the PCs are all faction members. Have them pick one, assume one of its ideals and take a bond with their immediate supervisor, should such a thing be applicable. Membership in a faction is secret, but, because of the current situation, they've all been assigned to work together. They already know each other. They are investigating cult activity in the region on behalf of their (now cooperating) factions. Begin scene Greenest Arms (below).
The PCs are in the inn, on the west side of town. Just pick a likely building from the HDQ map of Greenest. Ask them if they're:
Eating and drinking
In the upstairs rooms, amorously
In the upstairs rooms, meditatively
On the balcony, reflectively
At the stage, listening to the (avant-garde / terrible / heartthrob / intoxicated) bard
At the bar, asking for info about cult activity
Once you know who's where, tell them they hear screams, and, when they look out the window (or balcony), they:
see people running to the keep
hear screams and see figures moving in the distance
see distant fires
People in the inn start yelling to get to the keep; there's a raid. They know the drill. Then start the raid turn.
What are the players doing? Holing up or moving? If they're holing up, use the holed up procedure below. If they're moving, proceed.
Ask how they're moving:
off road or in cover: 1/6 encounter chance
in housing block: 2/6 encounter chance
on road: 3/6 encounter chance
around important structures (mill, smith, store, inn): 4/6 encounter chance
around refuge (church, manor, keep): 5/6 encounter chance
Ask if they intervene or keep moving. If they intervene, resolve as normal. Otherwise, proceed.
If the dragon is here, check the table where is the dragon?
Check for unavoidable encounters using the same procedure as above. They can run, of course. Resolve the encounter as normal and proceed.
Greenest Arms is two moves away from the Keep. You can make a hexmap of the village if you want for this purpose. Otherwise, assume a move is about 200 feet.
Each movement turn is 10 minutes. Each holed up turn is an hour.
If they get to the Authority (in the keep/manor/church), the Authority will likely have missions for the PCs that will grant them no immediate benefit. But they can be heroes if they want. Just use the missions from the module: saving people at important structures, getting prisoners, driving away the dragon if the dragon is present.
NOW FOR SOME PROCEDURES & TABLES
What's the situation? 2d6:
2: worst possible (the most important place in town has been breached / slaughter commencing or nearly over)
3-5: worse than you expect (the most important place in view is surrounded / aflame, large group of people suffering)
6-8: what you expect, given the progess of the siege (chaos, people running around being slain, looting of houses, stacking bodies, wrapping up and loading the treasure, etc.)
9-11: better than you expect (a group of militia fighting back, the coast is clear, survivors running to the woods without pursuit)
12: best possible (the siege is ring called off early, or the forces are engaged in a tactical retreat—what magic is afoot?)
The people want (when things calm down or place isn't besieged):
the children to stop going missing
the lord to stop taking the loveliest youths
the crops to stop purpling, crisping, and floating away as ash
the dead to stop clawing up
the ancestors to stop haunting in their preachy and nagging way
the bandits to stop stealing our crops—won't make it the winter this time
the boys and girls alike to stop coming home pregnant from the forest
the other sect to abide by the ban on their worship
the fields to be rid of the 6-18' long muscular tooth-mawed worms
their prized chocobos to return to their stables; something scares them, and they won't enter the village
to stop lying compulsively about everything
the river to un-petrify
the bronze clouds above to melt and let the sun shrine through again
the body parts to quit floating down from upriver
the trees to stop screaming
the heavy special tax nullified—what is the lord building with the money anyway?
to have enough food that hibernation isn't necessary after this year's harvest
to drown the lord in a bathtub of his own vodka
to subdue and despoil their intolerable neighbors
the plague to stop
The Authority wants / from (d6, twice):
Money / the people
Respect / peers
Compliance / superiors
Revenge / enemy
Cover / allies
Love / family
Why can't this person get what he wants from the other person (2d6):
2: Lacks unreasonable virtue
3-5: Lacks secondary virtue
6-8: Lacks primary virtue
9-11: Other person unreasonable
At the start of the turn when the party is holed up somewhere, make a reaction roll:
Very context dependent here. If the PCs barely made it in and are holding the doors against an actively opposing force, a bad result means, in addition I whatever opposed do-they-break-through checks you might do in the round, a boarded up window breaks, and a villager gets shot through it.
If the PCs are holed up somewhere and no one saw them, the worst thing is that they're discovered. Bad would be a group of monsters encamped nearby. Etc. Good would mean maybe some militia passes by you can link up with.
Where is the dragon? (2d6)
2: coming right for you
3-5: headed your way
6-8: staying where he is
9-11: heading away from you
12: leaving (for now anyway)
Checking for survivors:
Players commit to the search for the given amount of time
GM determines how likely it is or there to be survivors here (x in 6, definitely, or definitely not)
GM checks, but doesn't reveal if there are survivors
Random encounters checked for, if any hostiles may still be in the area, and those encounters resolved
GM determines how likely it is, given then time, method, and area the players are searching, for them to find survivors
If none are found (whether there are any or not to find), GM asks what they want to do now. Players can repeat the search, modify it, abandon it, what have you.
If survivors are found, check the d20 table on the village encounters roll all the dice table to see what kind of group is encounters
Use reaction roll to check their mental and physical health