After Twilight becomes the new ruler of Equestria, God sends Archangel Michael to guide her along her ways until she follows the right path. But when his archenemy, Satan keeps showing up to disturb him on his duties, he wishes for a way to destroy his enemy.
Angels, having no free will, cannot do something unless their Creator specifically tells them to do so. But Michael is determined to find a way, and Twilight may be the key.
(As you can tell from the cover art, the angels and demons here will not look like the traditional depictions, they will look more akin to the 'biblically accurate angels' art you see online.)