I really like the idea of a man tracking down a homeless guy to give him money. Sounds fun. I think someone NOT a PI could be more fun, though. PI's are already in a grungy environment, no? Why not someone who's used to white collar work, like an attorney or something? The family's attorney is tasked with hunting down the homeless guy before ___ date if he wants to collect his money.

This idea could easily be turned into a thriller. What if the homeless guy is suffering from amnesia, and after getting proper care, begins to remember a horrific event, like a hit-and-run or a blood bath of some kind? He comes back to the PI not for friendship, but for help in doing something with the information he has. Yes, something with a similar feel has been done before..."Caveman's Valentine." However, this could be far different with respect to the protagonist's arc.