The title of the episode is likely a reference to the Biblical Four Horsemen of the Apocalypse. Though it would make more sense if the episode title was "The Fourth Horseman" since the fourth horseman is death. The third horseman is famine, which doesn't make much sense considering the context of the episode.
Robert Stanton (Dennis Griscom) also played the role of Mr. Nower in Episode 9.16, Three-in-One (2010).
Phyllis Somerville (Mrs. McLeish) also played the role of Louise Politano in Episode 3.16, The Saint (2004).