"Thendara House" is a sequel, of sorts, to the previous Darkover novel "The Shattered Chain." The reason I say "of sorts" is that Bradley has always intended for each Darkover novel to work as standalone novel. The events of "Thendara House" just happen to be set after those in "The Shattered Chain" and continue the story introduced in that novel. This is a novel of the Renunciates, an order of women who have rejected society's role for them and exist as a societal alternative for women.
This novel switches between the viewpoints of two characters: Magda Lorne and Jaelle n'ha Melora. Magda, or Margali as she is called by the Darkovan natives, is of Terran heritage (and is an employee of the Terran Empire), but she was raised on Darkover since she was a child. During the events of "The Shattered Chain", Magda took the Oath of the Renunciates under duress when she was trying to rescue her former husband, Peter Haldane. By the end of that novel, she decided to honor that Oath and came to believe in it. Thendara House is the chapterhouse of the Order of the Renunciates and Magda is to spend the next six months in training at Thendara learning the ways of the Renunciates. Jaelle is the Renunciate who took Magda's oath (this is a special relationship). In order for Magda to be able to fulfill her obligations, Jaelle agreed to work at the Terran spaceport for the 6 months that Magda is at Thendara. Magda is also now married to Peter Haldane, Magda's ex-husband. Peter, like Magda, is a Terran citizen who was raised on Darkover and works for the Empire.
Neither woman truly belongs where she is. Jaelle feels alienation because she is a Darkovan working at the Spaceport and everything she is experiencing is new and different and strange to her. Her relationship with her husband is also becoming strained as she is still struggling against those gender roles she had thought she left behind when she joined the Renunciates. Magda knows that she can never truly belong to the Renunciates because she is Terran and, at least for a time, she has to hide who she really is to fit in at all.
"Thendara House" is a more complex novel than it at first seems to be. Bradley works through the ideas of belonging to a culture and what happens to those cultural transplants which are put into a new and different environment. She works with the friendships between women and the complex relationships that women can have, both casual and intimate. "Thendara House" is the best of the seven Darkover novels that I have read so far and this came as a pleasant surprise to me.