The Cure was a potion that could cure immortality. It was created by Qetsiyah as a way to allow Silas to be cured of immortality in order to die and be with the witch Qetsiyah for eternity. It was hidden in a tomb in the depths of an island off the coast of Nova Scotia, along with Silas' body; both could be found with the map hidden in the Hunter's Mark. The mark, upon completion, also reveals a spell that can unearth Silas and the cure from its hidden cave.
Only a descendant of Qetsiyah, a Bennett witch, can perform the aforementioned spell. There is only one dose of the cure.