Phormio is a Latin comic play by the early Roman playwright Terence, based on a now lost play by Apollodorus of Carystus entitled Epidikazomenos ("The Claimant"). It is generally believed to be Terence's fourth play. It was first performed at the Ludi Romani of 161 BC. Structurally, Phormio is considered to be one of the best Roman comedies. The plot is set in Athens, and revolves around the love affairs of two young men, Phaedria and Antipho, who are cousins. Phaedria is in love with a harp- player called Pamphila, but doesn't have the money to buy her from her owner Dorio; Antipho wishes to marry a free but poor girl called Phanium, unaware that she is in fact Phaedria's half sister as the result of an affair between Phaedria's father Chremes and a Lemnian woman. By clever legal wrangling, Phormio manages to help both young men to obtain their wishes, and in addition extracts a large sum of money from the two fathers. Note: Inline page numbers refer to [1].

References:
https://en.wikipedia.org/wiki/Phormio_(play). https://en.wikipedia.org/wiki/Phormio_(play) Terence. (1976). The Comedies (B. Radice, Trans.). Penguin Classics.