Black Swan (AU Captain Swan fanfic/OUAT)

When a new threat comes to Storybrooke, what new challenges will the residents have to conquer? And at what cost will it take to rid of the threat?

•This fanfic is as stated, an Alternate Universe piece, so the plot and characters don't match exactly as the series does. The idea and plot concept is mine so please don't take it unless you ask as I put effort into making this story•