Trapped in an underwater cave, a group of academics must face a series of deadly, supernatural trials—each one demanding they confront their darkest sins—in this chilling aquatic cult horror debut from Megan Bontrager.

Grad student Caro has no idea what she wants to do with her life, but when an opportunity arises to act as a research assistant on an anthropological expedition for her professor and lover, Edward Beck, she doesn't hesitate. Beck assembles a team of academics and professionals to study the ancient sea-based Cult of the Leviathan, and the expedition descends into the sea caves where the cult is said to have dwelt.

But when the cave entrance collapses, trapping them inside, the expedition finds they are not alone in the darkness. Surrounded by strange artifacts and scattered bones, an ancient trial has been set in motion. One by one, the members of the expedition will be tested and forced to atone for their greatest sin. . . or die.