Expelled from her prestigious boarding school, eighteen-year-old Lark returns home in disgrace to discover her family on the brink of financial ruin. Desperate to save them, she accepts a marriage of convenience ... to Therion, an underworld god worshipped by Lark's isolated coastal hometown. Her only hope is to seek help from Alastair Felimath, the brilliant, arrogant boy who was her first heartbreak, and his alluring older sister, Camille. As the trio delves into the folklore of the gods, Lark falls under the spell of the Felimath siblings. Ensnared by a fervent romance, they perform a hedonistic ritual to repair the connection between Lark and her bridegroom. Instead, they draw the ire of something much darker, which seeks to destroy Therion - and Lark as well.