At this point, the group has recovered five of the six draconian relics. If they're paying attention, they've noticed that there's one missing -- the twin of the giant horrible undead-producing sword that Martha had back in Scene 1.
This artifact is held by Brother Sandscour, and he's in a warehouse somewhere in the village. He's sending zombies out to capture people alive, and the zombies are dragging the people back to his warehouse, where he kills them and turns them into more zombies.
In this scene, the player characters track him down and kill him.
(If it's getting late and your group is running out of steam, it's okay to skip this scene. If you're skipping the scene, assume that Brother Sandscour has left the village, and isn't actively killing people, and tell the group that tracking him down is an adventure for another day.)Tracking him down is pretty easy. The group comes upon a pair of zombies dragging a civilian between them. "Help!" says the civilian. If the group follows the zombies, the zombies lead them to the warehouse. Other methods of tracking, like aerial scouting for concentrations of zombies, or just following the zombie tracks, will also work.
Set up the board for the final battle. Draw a big square, with a ten-foot-wide door, to represent the warehouse. Scatter zombies all over the board -- you want enough zombies that "okay we'll just fight all the zombies" is clearly not the right way to solve this combat. If the group has any method of scouting, show the interior of the warehouse, with Brother Sandscour in the back, holding the artifact weapon. The warehouse has two internal columns holding the roof up, and it's full of zombies. The artifact weapon is in control, but Brother Sandscour is willing and cooperating.
The best way to solve this battle is to hit Sandscour's weapon with Stonecrusher, destroying it, which also destroys all the zombies it was controlling. If the group doesn't think of that, another approach is to collapse the building on him, which won't kill him but will kill the zombies. (And he'll have to pull himself out of the rubble, which takes time.) If the group doesn't do that either, they'll have to actually fight him.
Fighting him will mean disarming him, keeping him away from the weapon so he can't pick it up again, and slowly chipping away at his hit points. If the group lures him on top of a building, they can have a mostly zombie-free battle: the zombies do eventually climb the building but it takes a long time.
Some groups will disarm Sandscour and then pick up his weapon themselves. With some good mental checks, it's possible to take control of Sandscour's zombies and command them to destroy Sandscour (or destroy themselves). This has the obvious risk of getting controlled by the weapon.
If somebody thinks of another good plan, try hard to let it work.