Prelude: The Rescue of Lord Erkenfried

The heroes had been taken by surprise by the scale of the explosion. Not only did it seem that the enemy had somehow managed to get inside Ailech, but they had also struck a blow from which the defense of the city could not possibly recover.
A handful of refugees fleeing from the Westgeat hysterically described the enemy as monstrous and infernal, interested in nothing except inflicting pain, suffering and death to every living creature they could find. "Black Moon Incarnate", Bishop Guire muttered almost to himself, "I have fought their like before. The people of this city will need help, and soon".
A fleeing soldier described how strange winged beasts of flesh and stone had dropped from the sky to attack the guards on the Keep walls while inside the buildings an insidious fog had formed across the floor which inexorably rose until it was at knee height. Before anyone could comprehend the foulness of the corrupt magicks already being wrought an enormous explosion of green and blue fire crashed from the bowels of the Keep and ripped through the whole building levelling walls and caving in roofs and doorways. Lord Erkenfried himself rallied the defenders but something reached out of the fog, dragged him to the floor and stole off with him to the Western quarter of the city.
Rescue did not seem possible to the heroes. Demons were prowling the streets, a matter of hours would see the forces of Unlife within the city walls and any defence had already been destroyed or neutralised by magical corruption. However, Kronin had not been paid, Siriel feared for the souls of any elves still alive within the walls and Bishop Guire knew that if the evil could not be contained and then stopped all of Talomir would fall to the Black Moon. As Throrin put it, "Certainty of death, small chance of success... What are we waiting for?"
The demi-human warriors turned quickly to the ropes that had been left for their return from the mission to the enemy siege lines. The bishop and his retinue turned eastward along the wall seeking out a postern that he was certain he had seen earlier as they left the city. Climbing into the city proved harder than expected without the aid of the guardsmen on the wall. Thali proved to be the first casualty of Kronin's expedition as he fell from the wall with a sickening crunch. With Thali's death the others climbing the wall were more careful. Consequently, both the elven and dwarven bands ended up parted by the high city walls.
Things were not going to plan, Kronin could see Black Moon horde moving towards him and the sharp eyed Siriel was certain that something large and winged was moving through the maze of damaged and ruined buildings. Still there was no sign of Bishop Guire.
Demons came forward through the rubble and a minor demon revealed himself as the leader of the horde closest to the Westgeat. Raising a great clawed fist and speaking in the guttural tongue of the Black Moon Cant it cast a bolt of infernal flame into the midst of the dwarven band. The warriors scattered but not before two more dwarfs were slain, their souls burned from their mortal forms.
Suddenly, the Bishop's men arrived from the eastern end of the quarter. He quickly moved to intercept those demons that could be seen. They seemed to be led by an abomination, part man, part demon. The freakish monstrosity cast a spell exhorting his horde to charge the Border Kingdoms retinue. The spell worked as the horde of brutish horrors let out a roar of defiance and rushed forward but only their possessed master made it to the line. The remaining humans reacted quickly and surrounded the possessed mage. The combat was short and resulted in the isolated mage being cut down. Before they could reorganise to meet the oncoming threat, an inhuman demon strode across the ruins and fired a ball of diabolical flame into the midst of the retinue. Several men fell, especially among the poorly armoured Borderers but nobody panicked. The Bishop let out a roar praising the power of the Red Sun and charged towards the demon. Sensing the righteous wrath within the Bishop the demon fled.
Back at the western end of the city quarter the dwarves and elves had prepared themselves to meet the demonic forces arrayed against them, even pre-empting the charge of the horde and bringing down several of them with axe and longbow. The minor demon screamed in rage and leapt into the fight cutting down another of Kronin's band and injuring one of the elves. Driving the demon off momentarily the elves used the respite to fire a volley of  arrows, one of which luckily found its mark. The demon screamed in pain and seemed to be consumed by the same green flame it had used only minutes before against the dwarves.
As the Bishop and his retinue finished cutting down the last of the horde, the warbands split up to search the buildings for the hopefully still living Lord Erkenfried.
The Bishop found the Lord held at dagger point by another of the possessed cultists. Attempting to cast his malevolent magic against the Bishop and his retinue, a misplaced word or gesture resulted in utter failure and the cursed mage paid the price as he was dragged screaming beyond the Veil into the Unlife.
The heroes worked their way back to the unguarded Westgeat and made their escape along the Fortrenn road. Hopefully the bridge would still be there...