Character A is a concerned neighbor. So of course he called the cops when he heard muffled gunshots from next door. However, the cops didn't arrive next door - rather, someone arrived at his door. And they certainly weren't cops.
It's a mafia themed story. Character A is a journalist having recently moved in to a shady neighborhood. Unbeknownst to him, Character B, whom he had been trying to expose (who is the head of the mafia) owns the area.
So Character A was home alone one night. It's pretty late, probably after 12 o'clock when he heard the gunshots. He then decided to check out what's going on. He overheard his neighbor on the phone (who's working for Character B) that he needed someone (from the gang) to come over and help to dispose the dead body. Character A, terrified, scrambles off to his house, not knowing that his neighbor noticed him, barricaded his house and called the cops. His neighbor informed Character B about Character A, and Character B decided to matters to their hands.
So far, that's the only thing that I can come up for the introduction. I have plenty of ideas for the later parts of the story, such as Character A and Character B working together to take down another rival gang in exchange for Character B to protect Character A from danger (I'd like to think that Character A got in trouble for trying to expose a corrupt politician and asked Character B for help) and Character A not exposing Character B's business. Blah blah blah, they fell in love, blah blah blah, more drama, conflict, blah blah blah a happy ending?
My current idea is for Character B to spare Character A's life that night and promises to set Character A free, but I don't have any reason why yet. If you guys could help me out, I would be really grateful!