An undercover policeman, Michele Rossi, infiltrated in a major criminal organisation, is ambushed and killed by two mysterious professional killers. Inspector Terzani, a close friend of the victim, disobeys Gori's orders and conducts his own investigation. In incognito, Terzani and Rex get themselves admitted as patients in a luxurious private clinic run by an important specialist, Dr. Nevio Cangelosi.