During a traumatic accident on a deep-sea dive, Olive, a gifted, young marine-biologist discovers an unearthly creature. Losing her dream job, Olive smuggles the creature home, intent on studying it in secret, unbeknownst to her devoted boyfriend Matt and estranged sister Ellie. Plagued by gruesome nightmares, her fractured memories of what happened in the depths of the ocean begin to unravel, revealing her symbiotic bond with an eldritch horror far older and malevolent than she could possibly imagine.