The Rules of Fair Play Do Not Apply

Fill for this prompt. Because I cannot resist Jim Moriarty, no matter how hard I try. Basically, only the first hostage in TGG happened, because Sherlock called Jim and then they decided it would be more fun to keep each other entertained. Jim starts hanging out at the flat, and begins to think John is pretty interesting. Sherlock and Jim begin competing over John and trying to ruin one another's attempts to woo him.