Depending on Geralt's choice of guardian for Alvin in Act III, he either receives a letter from Shani or from Triss when he meets Jaskier in Aguas Turbias as part of the Alvin quest.
Depending on Geralt's choice of guardian for Alvin in Act III, he either receives a letter from Shani or from Triss when he meets Jaskier in Aguas Turbias as part of the Alvin quest.