[2] The original cast included Barton Booth as Omphales, John Mills as Zimon, Colley Cibber as Tryphon, Charles Williams as Ammon and Mary Porter as Hesione.
In ancient Greece, a man, Ammon, is upset that his adopted sister, Hesione, whom he is in love with, is going to marry a soldier, Omphales.
Ammon decides to blackmail a priest, Zimon, who is officiating the wedding of Omphales and Hesione, into delivering a bad omen that will prevent the two from marrying one another.
Omphales leaves the city and conjures up an army of soldiers to overtake Tryphon, but is, along with his allies, defeated and killed.
The prologue to the play states that The Fatal Constancy resembles ancient Greek drama in its structure.