Two things kept repeating over and over in my head as I started coloring this. Skin as pale as the moon, and a tail as dark as night.
I can see a recently discharged John moving to a coastal town, and moving in as a tenant for the elderly Mrs. Hudson who also runs the deli next door. John takes up free diving to keep in shape and not aggravate his injuries too much.
There are old tales about the sea creatures told by the fishermen. One of them being that if you are alone at night you can hear a violin being played down by the shore. However, if you try to see who is playing, the music will stop, and no one will be there when you get to the spot you heard the music coming from.