Brightmoon is a town that does what it must to survive. This bleak age, where so many of the spirits of the dead wander the night, sees so many of the bodies of the deceased animate spontaineously that burial is impractical: burial grounds become swamped with the walking dead, so that digging is dangerous, and the dead can too easily walk over to the living; burning wood for every plague- or starvation-slain peasant is too costly; and simple dismemberment brings undertakers in close enough contact that whatever curse animates the dead begins to affect them as well. For that reason, only dumping the bodies in the sewers beneath the haunted Temple has allowed the people reasonable safety from the deceased. As such, the sewers are a most perilous place to travel.
The party had just escaped the Hobgoblins above with the prisoner Palo, a member of the Holy Order of the Golden Chalice and, of all things, a Tiefling at that. Following a map towards an escape tunnel, hopefully leading them out of the city's limits and beyond the reach of the Goblins, they decided to risk the dead in the sewers rather than sneak and avoid the guards in the city above. This was fairly straightforward, as most of the walking dead were simple zombies, easily dispatched.
Along the twists and turns, the party found one of the ghosts of the priests that haunted the Temple of the Lost Gods, the Haunted Temple. It seemed to be unravelling strangely, like a wool sweater coming unknit. With a mournful wail it told of a dark stranger with dark magics in the temple, before it vanished.
The party decided to investigate, and made their way to where the temple would be in the streets above. The tunnels beneath the temple were a catacomb, built long before the sewers, it seemed, and blocked off from them by a gate. Where the sewers were slime-slick stone and rivers of waste, the catacomb waters were pure and clear, the stones pale white marble. There were many carved-out holes where bodies were placed, beneath the water line when the sewer had flooded in, though becoming pure water when it crossed the threshold. A long stair led up to the Temple above, where from could be heard a strange, horrific horn blowing.
Getting up to the main level, the party saw a Tiefling spellcaster in the middle of a magic circle. This Tiefling was hideous, covered in boils and sores that, upon closer inspection, opened and closed as alien eyes and fanged mouths. Around the circle were large, alien statues of strange tentacled beasts, hideous creatures of green stone. Off to the side was a row of circles, each holding a ghost trapped. As the Tiefling continued to chant, one ghost disappeared from one spot to appear in the circle; then, destroyed in a faster version of what afflicted the sewer ghost below, a strange alien creature, like the ones depicted by the statues but only the size of a man, appeared in its place.
The party charged to attack. Strange energies from the statues slowed them, and the bizarre creatures afflicted them with poisonous stings that halted them in place. Only team work and luck allowed them to prevail: the Eladrin Swordmage Lady Audacia made her way to the Ghosts and freed them by destroying the magic circle around them, while the others slew the Tiefling and what creatures they could.
As the ritual was undone, the party was overcome by a wave of madness and nausea. It seemed that the statues came to life, unfurling great wings of leathery skin, and lifting into the sky, their smaller versions doing likewise and following them. After this, the party were knocked unconscious, swallowed by the darkness of sleep.
When they finally awoke, Palo was tending their wounds. It was dawn, and the daylight that made it through thick clouds was just enough to dispel the horrors of the night before. They healed as best they could, as the ghosts would return to haunt the temple. He gave a brief explaination of himself, and answered that his brother, the one who sent them on the quest to rescue him, was in fact Lucius of the Order of the Chain! He had been spying for the Holy Order, giving locations of plans of true horror for his leaders to act upon, when he was finally found out. He was weak, and not a powerful cleric or Paladin, but he could help them heal in times of trouble, and give what knowledge he could to aide them. He helped Oonagh identify the Horrific Rod of the Tiefling Warlock, and some other items they'd found, including a bag of eyeballs that would allow the user to see through them for a short time.
With that, the party resolved to continue down through the sewer to the mysterious tunnel on the map, and left the Temple to its ghosts.