The Rainbow Scorpion oleh Keith E. Smith

A cartel controls production, pricing, and distribution of its products by thoroughly eliminating any and all competition. Though he had been a high ranking member of the cartel for years, Antonio Vargas was certain the cartel now viewed him as competition. An unlikely and unique friendship is formed when Antonio enlists the aid of Kelvin Ray Elliott, a retired mathematics instructor, to help free him from the cartel, and save the lives of his daughter and grandson.