Wrath of the Demon Lord

From the description:

The town of Ravenshead has fallen to dark forces. During the last new moon, demons poured forth from the cathedral’s crypts and slaughtered the townsfolk. Now, the few surviving villagers have fled to a nearby town in search of help. Fearing that the demonic invasion might flow out into nearby settlements, the local constabulary have offered a reward to whoever can close the portal allowing them into our world.

Unbeknownst to most, a portal was opened by the local clergy when they read from a forbidden book found deep beneath the cathedral. This has allowed a Pit Lord to take up residence in the crypts and summon forth more demonic henchmen.