If this is too late for your session, perhaps you can use it later.
Since the religious aspect seems important in your saga:
The Covenant needs to send out a group to a village close by, perhaps they need to contact someone, or to get some supplies. One person knows this village is known for a shrine to a local minor saint. Another has heard of the wicked and sinfull ways of many villagers. A third knows the village has some important resource, produced some goods needed or has a usefull artisan. Arriving at the village, they see it enveloped in a strange mist, and hardly emit a sound. Insode the village, people seem quiet and depressed, moving in trance like states about their business, barely acknowledging any other. Only sound and light comes from the tavern, where drinking, gambling, whoring and fighting is going on in the tavern. Every time the PCs come in there, things escalate. If there is someone with a relevant supernatural ability (Sense Unholiness, Second Sight), he sees it first, otherwise the person most pious: Small, demonic imps flock aorund the sinners, apparently unseen by them, egging them on, whsipering in their ear, manipulating items to cause trouble (spill my ale will you! ). Outside, impa are also seen in the village, often making contact with the depressed people, spurring them to join the "fun" in the tavern or to sin and perform utterly selfish and malicious acts. Trying to clear this out might involve talking directly to the prople, but the sinners are almost too far gone, and the other villagers are in despair. Magic could get rid of the imps, but only temporary. The less pious PCs should start to get tempted, depending on their Personality Traits. At some point, the demon responsible for this corruption, will start to act directly. He will cause minor disturbances (fires, lynch mobs, animals gone berserk), framing the PCs for it and force villagers to violent actions. Eventually, he'll start turning people to stone (hopefully before the PCs get a clear fix on who and what is doing this), to save the humans for a day, where corruption is brought on easier. He might be invisible, just for the heck of it. The story might end tragically, with the villagers turned to stone, and the demon moved along. Many may die, and the vilage could burn down. On the other hand, the situation could be resolved with varying degrees of succes, earning the Village as a place of contacts, resources, workforce or even friends to the covenant/PCs.
Some of this is lightly based on my vague recollections of a Twilight episode for the entire cast of magi, in my first (4th ed) saga. Someone else was running the story, hence my vague memory, it was played perhaps 10 years ago. But it seems like a doable story, i might even run this myself. Demonic corruption is always a good theme, although not in every story.
ope this inspires someone.