Child of the Elder Blood is a main quest in Skellige and part of Battle Preparations. Ciri pulls Geralt aside for a private talk: Avallac’h has a hidden lair that even she, his star pupil and long-time companion, was never allowed to visit. On the eve of the final battle, when everyone has to trust each other completely, that is not a comfortable thought.
Geralt and Ciri travel to the Pali Gap coast and break into the Sage’s hideout, guarded by a golem. Inside they find a secret laboratory where Avallac’h has been studying the gene of Lara Dorren, the Elder Blood that Ciri carries and that is the source of both her power and her misfortune. Ciri is, understandably, not pleased to find herself the subject of research.
How Geralt reacts matters. He can encourage Ciri to talk it through with Avallac’h, or he can let her anger take over. That choice is one of the small but important moments that shape how Ciri sees herself, and it counts towards the ending of the game.