Dr. Sara Holt spends her days mediating toxic relationships, but when an apocalyptic outbreak engulfs the skyline, she finds herself barricaded on the top floor with three bickering couples ready to kill one another. Her professional neutrality fractures completely when the final refugee pounding on the reinforced shelter door turns out to be Mark, the spiteful ex-husband she divorced months ago.
With bloodthirsty hordes clawing up the stairwells and dwindling food rations provoking furious shouting matches, Sara is forced to ration supplies while managing volatile domestic disputes. Mark tries to leverage their shared past to regain her trust, forcing Sara to confront old betrayals while maintaining order before petty marital hatred gets everyone slaughtered.
