Virginia City is visited by one Thomas Crippen (Ashley Cowan), an Englishman who has travelled all over the world in search of the man who "murdered" his wife on the operating table. Crippen is convinced that a doctor named Mundy is guilty of the crime-and as it turns out, Mundy is the real name of Professor Poppy (Michael Rennie), a medicine showman whom Hoss Cartwright has befriended. Partially based on fact, "Once a Doctor" was written by Martha Wilkerson. The episode first aired on February 28, 1965. ~ Hal Erickson, Rovi