“I see a bad moon a-rising. I see trouble on the way.”
If you don’t know this song, give it a listen, absorb the lyrics, set the mood in your mind.
Now, what does the bad moon look like? What does it mean? Is it a prediction or a curse? Is it only in effect that night while the moon is out, or does it reach far beyond?
Go forth and write! And feel free to put links to work birthed from this prompt in the comments below.