After a global apocalypse has decimated the human population, the only survivors are two childhood friends: Billy, the former President of the United States, and Ray, a scientist who was once Billy's adviser. Carrying the weight of guilt for his perceived role in causing the apocalypse, Billy and Ray find solace in a protective dome constructed by Ray that shields them from the harsh realities of the outside world. They maintain a modest fishpond, but unease sets in when the last surviving female fish dies, leaving them with only two male fish, one of which is showing signs of distress.
One night, while working late, Ray stumbles upon a fascinating discovery: the remaining fish appear to be undergoing sequential hermaphroditism, a process that allows them to change sex to continue breeding. To his astonishment, he notices a vivid green light shining outside the dome. The following morning, Ray shares his findings with Billy, only for Billy to realize that he too is undergoing sequential hermaphroditism, which means his body is gradually developing female characteristics.
This revelation leaves Billy feeling distraught about the changes overtaking his body, while Ray becomes increasingly fascinated by the phenomenon. However, their dynamic shifts as Ray finds himself uncomfortable when he touches Billy, particularly when physical intimacy leads to unexpected feelings of arousal. As the fish begin to breed, Billy confides in Ray that he has started menstruating and suggests that they consider having a child together. Struggling with deep-seated homophobic beliefs instilled in him during his upbringing, Ray hesitates and pulls away from Billy, causing tension between the two.
Despite the emotional upheaval, their bond begins to strengthen when they decide to pursue intimacy with the aim of procreation. Their initial attempt is shrouded in modesty, with a sheet covering Billy, yet as the moment unfolds, Ray's reservations dissolve, and they share a kiss. Soon after, Billy finds out he is pregnant, and this development brings them closer together.
Their newfound intimacy faces a significant challenge when a fierce storm hits, shattering the dome's windows and forcing them to dismantle the fishpond in a desperate attempt to seal the breaches. The subsequent morning brings a surprising sense of awe as they witness the aurora borealis lighting up the sky, a sign that the weather may be shifting. However, the reality of their dwindling food supply compounds Ray's distress as the death of their fish takes its toll. In a moment of encouragement, Billy recalls a story from Ray's eighth birthday, urging Ray to cling to hope amidst their uncertain future.
