Vanity's Brood

The third and final volume in the House of Serpents trilogy, from New York Times–bestselling author Lisa Smedman
 
Medusanna is a priestess of terrifying power and ambition. Never satisfied, she convinces the Se’sehen—a yuan-ti tribe from the distant jungles of Chult—to serve her growing cult of Sseth, who specialize in dangerous games of deception, poison, and murder.
 
It is in the Sseth’s foul plane of Smaragh that Karell, a yuan-ti half-blood, lies trapped and desperate. Her only hope for rescue and survival is Arvin, a mind-mage of growing psionic gifts. But time is quickly running out for Arvin to find her—and with each passing minute, the House of Serpents slithers closer to destroying their last hope for freedom.