Mannix has finally quit the detective agency for good and is out on his own. The second season begins when Mannix encounters a deaf woman who has witnesses a criminal talking at a pay telephone, discussing a kidnapping. She has made out certain key words because of her ability to read lips. Mannix gets her to remember enough of the conversation so that he can proceed in his investigation. The detective finds a rich man who says his wife has been kidnapped. It turns out the rich man has really hired the criminal to kill his wife and make it look like a kidnapping - and the criminal is anxious to tie up all loose ends, including Mannix and the deaf woman.
—Bill Koenig