Appearance and Character
A Storm of Swords
Septa Nysterica accompanies Lady Margaery Tyrell to King's Landing for her wedding to King Joffrey I Baratheon. Sansa Stark meets Septa Nysterica, along with Margaery's other ladies, when she is invited to a supper at the Maidenvault.
A Feast for Crows
After Ser Osney Kettleblack comes forward with claims that he slept with Margaery, Nysterica is one of four septas to examine her maidenhead. The four septas find the maidenhead not intact, which becomes the grounds for Margaery's arrest. Nysterica is confined to a penitent's cell for failure to do her duty.