The two details from Jane Austen's Pride and Prejudice that are included in Mary Keith A Play are:
- The opening line, "It is a truth universally acknowledged, that a single man in possession of a good fortune, must be in want of a wife."
- The mention of Netherfield Park being taken by a young man of large fortune from the north of England who came to see the place and agreed with Mr. Morris immediately.
In the first line, this is a well-known introduction to the themes of marriage and social status in Austen's novel and it appears to be retained in Mackaye's play as an essential part of the narrative.
In the second line, this is about the arrival of a wealthy man in the neighborhood and his intention to take possession of Netherfield Park is also present in Mackaye's adaptation and mirrors the early plot developments in Austen's novel.
These two specific details indicate that Mackaye's play is closely inspired by Jane Austen's Pride and Prejudice and thus retaines key elements from the original text.