It's the winter solstice in a Philadelphia that has been eroded by extreme weather, economic collapse, and disease-carrying mosquitoes. The Saturnalia carnival is about to begin - an evening on which nearly everyone, rich or poor, forgets their troubles for a moment. For Nina, Saturnalia is simply a cruel reminder of the night that changed everything for her. It's now three years since she walked away from the elite Saturn Club, with its genteel debauchery, arcane pecking order, and winking interest in alchemy and the occult. Since then, she's led an isolated life, eking out a living telling fortunes with her Saturn Club tarot deck. But when she gets a chance call from Max, her last remaining friend from the Saturn Club, Nina will put on a dress of blackest black and attend the Club's wild solstice masquerade, the biggest party of the year, on a mysterious errand she can't say no to. Before the night is over, she will become the custodian of a horrifying secret - and the target of a mysterious hunter. As Nina runs across an alternate Philadelphia balanced on a knife's edge between celebration and catastrophe - through parades, worship houses, museums, hidden mansions, and the place she once called home - she's forced to confront her past so she can finally take charge of her own, and perhaps everyone else's, future.