Medusanna, a priestess of terrifying power convinces the Se'sehen, a yuan-ti tribe from the distant jungles of Chult to serve her growing cult of Sseth, the merciless god of the serpent people who languishes in the foul plane ofSmaragh, where a trapped and desperate Karell can only hope Arvin will find her before the House of Serpents finally destroys their last hope for freedom.