Isaac is the person coming to stabilize Cyrus's condition... right?
A bit of worldbuilding here: Helene's mother, Makenea, is the who created the Kingkiller Poison and the one who developed the magical plants for the antidote. That's why there are magical plants in Thantopolis in the first place. And it's also why there aren't many left... as Makenea hasn't come to Thantopolis in a long time.