What is a good plot/solution this mystery story?

I have to produce a short movie for class, and my group decided on this mystery thing where this detective finds random notes signed 'from C', telling him to leave the city. When he goes to the agency the next day his three assistants (Carl, Connor, and Celia (get it?)) inform him that someone called about their house burning down.

The thing is, we're stuck there. We need some kind of plot twist b/c just a house burning down is really mundane. Something psychological, maybe? We need a conclusive ending to the entire thing as well, ending with someone (preferably a new character) being caught and having some kind of reason for the notes. Maybe someone who was supposedly burned in the house (name begins w/ a C). Obviously this is a really big request, but please help me?
Asked Mar 29, 2016

TIP: If it's not your answer to this question, please click "Leave a Comment" button under the question to communicate with the question owner.