One of the biggest differences between The Last Wish and Netflix's The Witcher is the appearance and backstory of Geralt's great love, Yennefer (played by Anya Chalotra). In the book, Yennefer does not appear until she meets Geralt in the last chapter. And aside from portraying her as a powerful sorceress, the book doesn't dive into any major details about her or her past.
But the show brings Yennefer's character into the fold from the beginning, and starts to tell her backstory from an earlier timeline. In an interview with BGR, showrunner Lauren Schmidt Hissrich said that "one of the biggest storytelling shifts" she made was introducing viewers to "Yennefer and Ciri before they meet Geralt."