"Angel" Story

An old story concept involving a young man falling to earth, resulting in amnesia. He doesn't know who he is or where he came from, but when demons begin appearing in the small town in which he's taken refuge, he reveals otherworldly powers of his own.

His friend concludes that he must be an angel, sent to protect the town from the invading demons. But is he truly a guardian angel? Or an angel of judgement? There's no way to tell until he remembers his mission...