I've vaguely planned out a scenario as follows:
An introduction during the Avernum-Empire wars, where the party are Imperial irregular troops, helping an attack on an Avernite outpost. Kill lots of avernite soldiers with help from a squad of troops, rescue tortured prisoners, etc. After all avernites are dead, Vahnatai will arrive in an endless stream, forcing the player to retreat.
Fast forward 10 years.
Party tours Praglad, visiting a peaceful town in a peaceful vale. Town is nice and decadent, and disdainful of the party. Perhaps racist. News of Avernites causing plagues in Valorium. Then an Avernite envoy arrives.
Now, divide into two paths. Player can switch paths up to a point, by persuing certain actions.
Path A:
Player kills the envoy, protecting the town.
Player is arrested by Mayor for disorder, but contacted and secretly released.
Player sneaks into Imperial fort, and talks to an old comrade. Is told that Prazac had been scared by Avernites into submission, and that he is part of a secret force to restore the integrity of the Empire.
Player ordered to attack Avernites taken on escorted tour around vale.
Player ordered to kill Imperial scouts assigned to lead group, and locate rogue Imperial army people.
Player ordered to attack main Avernite camp.
Player ordered to 'cleanse' town of Avernite influence.
Path B:
Player talks to envoy, learning of Avernum-Empire treaty.
Player leads delegation of Avernites, surviving 'bandit' ambushes.
Player survives assassination attempt.
Player accumulates evidence pointing to real source of attacks.
Player attacks base, killing big bad boss.
Currently 2% complete.