In a ruined world scarred by monsters and societal collapse, an aging wanderer named Agrippa rescues a young woman named Claudia from bandits near the isolated settlement of Mist. Reluctantly, Agrippa accompanies Claudia back to Mist, only to witness a massive, slug-like monstrosity crash through the settlement's walls. The creature infects the settlement with a deadly miasma, dooming the survivors to a slow death without a cure.

In the aftermath, a young man named Remus-idealistic and desperate to prove himself-volunteers to journey far to the north in search of the fabled Celestial City 66, a legendary sanctuary rumored to hold the technology to cure any disease. He is joined by Agrippa with precious silver as payment and Claudia, who refuses to let Remus go alone. The trio sets off across dangerous terrain, encountering ruthless warlords, horrifying grotesqueries, and the remnants of a lost world. Together, they uncover uncomfortable truths about their beliefs, survival, and human history.

During their travels, tensions flare and bonds are tested, as Remus and Claudia discover nobody outside of Mist has ever heard of Celestial City 66. Claudia and Remus, both inexperienced but determined, struggle to hold onto hope, while Agrippa guards his secrets under a veneer of indifference. The story weaves horror, dystopian decay, and coming-of-age grit-leading toward the perilous mystery of whether the Celestial City 66 even exists, and what awaits them if it does.