No Prep Module: The Valkyrie's Vengeance (Patreon)

The border town of Edrath  has long found itself the center of political tension between the  neighboring kingdoms, despite not being a valuable strategic location.  It's more likely to be razed in the event of war than conquered, an unsettling fate that a half-elf priest named Irann Blum believed was all too certain. In her desperation she beseeched the gods for help and was sent a glorious valkyrie to protect her town. However in time the valkyrie grew to despise the PC's neighboring kingdom and believed a holy war to purge the land of heathens is the only recourse. At least, that's what she tells adventurers.

In truth, Irann is a demon in disguise hoping to nudge the valkyrie to war prematurely by sending adventurers as assassins. The valkyrie Bartach believes the PC's kingdom is evil and corrupt and has been forming defensive alliances with smaller nations, but has not as of yet made motions towards war. Her death or provocation at this point would likely lead to a brutal war that would devastate all the kingdoms, a fact the demon Irann is trying to exploit.