Honor Among Thieves

What does a good cop do when his name and phone number is found in the pocket of a dead mobster from his past? Does he cooperate with the Internal Affairs investigator who wants to charge him with murder, but appears to have an ulterior motive? Does he launch his own investigation into this murder from another jurisdiction to clear his name and find the real killer?
Does learning that two former enemies have put a contract on his life complicate matters?