Pierce accepts an invitation to work on a case from a renowned environmental activist concerning a chain of abnormal neurological reactions in a group of young girls. However, upon examining the girls, Pierce discovers that a dark secret is at the root of their ailments. Meanwhile, Moretti questions Pierce’s motives in working on a case without her.

Moretti calls on Pierce to examine Elena Douglas, a woman who has confessed to murder and claims to be possessed by the Devil. Meanwhile, Donnie and Moretti’s wedding plans hit a bump in the road.