That someone is probably someone from Mars's past. Prometheus, maybe? The Witch, Prometheus and Mars were defenders of humani in the past, after all. Maybe the witch will persuade them both to defend the humani again. Maybe the witch at first will act as though she were helping Isis and Osiris, but since they are on the side of the Dark Elders, the witch will trick them after she get what she wants.
Don't worry. We only have 63 days left to wait!