The fight between Geralt and the Striga at the end of the episode depicts the same fight as is shown in the intro cinematic of The Witcher (2007).
Geralt's side of the plot, including the fight against the striga, are based on the short-story "The Witcher" from the book "The Last Wish".
This is not the first time actress Anna Shaffer plays a sorceress / witch - she had a minor role in the Harry Potter series as Romilda Vane, a Hogwarts student.
The longest episode of the season, with a runtime of 67 minutes.