All Things Seen and Unseen follows Alex Nguyen, an isolated, chronically ill university student in her early 20s. After a suicide attempt and subsequent lengthy hospitalization, she finds herself without a job, kicked out of campus housing, unable to afford school, and still struggling in the aftermath of a relationship's dissolution. Hope comes in the form of a rich high school friend who offers Alex a job housesitting at her family's empty summer mansion on a gulf island.

Surrounded by dense forest and ocean, in the increasingly oppressive heat of a 2010s summer, Alex must try to survive as an outsider in a remote, insular community; to navigate the awkward, unexpected beginnings of a possible new romance; and to live through the trauma she has repressed to survive, even as the memories -- and a series of increasingly unnerving events -- threaten to pull her back under the surface.