 McDiarmid took an early role as Mickey Hamilton, a killer intent on avenging the death of his wife and child in "The Professionals" for London Weekend Television.In 1990, he starred in the Central Independent Television series "Inspector Morse"'s episode "Masonic Mysteries" as the psychopathic con man Hugo DeVries.In 1997, McDiarmid played the villain, Ronald Hinks, in the "Touching Evil" two-part episode "Through the Clouds/The Lost Boys".