Netflix's The Witcher season 2 uses stories from the first book. The show is based on a number of novels and short story collections by Andrzej Sapkowski, the first of which was published in English in 2007 under the title The Last Wish. However, beyond serving as narrative inspiration, the reasons for incorporating existing Witcher stories actually help to explain some of the more subtle details of the show.
One story in the collection, "A Grain of Truth", sees Geralt encounter Nivellen, a beastly looking man who was cursed for raping a priestess and lives alone with the exception of a monster with whom he is in love. In the show, this encounter comes in the first episode of season 2 which bears the same name as the short story. Geralt and Ciri come across an abandoned village near a manor occupied by Nivellen, an old friend of Geralt. His cursed transformation leads them to discuss the nature of evil and Geralt's philosophy on what truly makes someone a monster. It's also revealed that the house is inhabited by Vereena, a predatory bruxa and Nivellen's lover. After realizing that the bruxa is satiating her taste for blood by preying on travelers to the empty village, a fight ensues in which Nivellen impales Vereena to save Geralt's life. As she dies, Vereena confesses that she truly does love Nivellen, and his curse is lifted, restoring his normal human form.
The reason that the show saves the Nivellen story for The Witcher season 2 is that it provides an ideal narrative to reacquaint viewers with Geralt's moral code. The modifications to the story, particularly Ciri's presence at the house, also allow her to bond with Geralt through stories from his past. The episode's complex moral implications also serve as a fitting first lesson for Ciri about being a witcher – a lesson made even more poignant by the connection to existing Witcher lore.
Geralt reminds the audience of his personal morality towards monsters through his interaction with Nivellen. The beastly-looking man initially claims that he was cursed for trashing a temple while high on mushrooms. Despite his seemingly good nature, his monstrous appearance has doomed him to be rejected by all society and live in solitude. His story reinforces one of the show's overarching themes, that what makes a monster is not one's visage, but rather their actions and motivations. It's a stark reminder to viewers going into season 2 that not all beasts are monsters, and not all humans are good.
Ciri's presence in the story is also significant to its placement in The Witcher season 2. It's the first chance for Ciri and Geralt to bond as she hears a story about him helping Nivellen years ago. It softens the gruff witcher and helps her to see past his tough exterior. The story's conclusion also teaches Ciri her first lesson about monsters. When she meets Vereena, the bruxa appears in human form and is friendly to Ciri before it's revealed that she feeds on innocent travelers and takes her frightening true form. After Vereena dies and Nivellen's curse is lifted, he reveals that he didn't just trash the temple, but raped the priestess who cursed him. It's very appropriate that the first new characters in The Witcher season 2 aren't as they seem, and this is the first time that Ciri understands how complex it is to identify a true monster. The lesson will be integral to her later training and even seems to inspire her desire to become a witcher.
Although "A Grain of Truth," appears in Sapkowski's first book, the story is even more effective for the Netflix show in season 2. Its placement not only allows for a fantastic introduction to the second season, but it seamlessly integrates some of the show's most important themes through an intriguing story. The lessons learned in it will continue to influence Ciri and other characters in The Witcher.