In search of a magic-using!John AU story

[melodyunity]

I only have vague memories of this story, but I have a yen to read it again. John is a witch or sorcerer or some other kind of magic user. I don't remember the plot exactly, but it involved two kids who were trying to raise a demon. I think the big confrontation happened at a dock by a river?

Does this ring any bells for anyone?