I'm not sure I follow the question. You hired a detective to report on an attorney and then that attorney (you think) helped the detective write the report, which defamed you? I am sure you are mis-using the word "defamed" so please explain how you believe were defamed. What are your damages?
I may be guessing or not licensed in your state. No atty/client relationship exists. I earn my living collecting points for "helpful" answers.