Flo and Clara, two students at the Brookhants School for Girls, are obsessed with each other and with a daring young writer named Mary MacLane, the author of a scandalous bestselling memoir. To show their devotion to Mary, the girls establish their own private club and call it the Plain Bad Heroine Society. Over a century later, the now abandoned and crumbling Brookhants is back in the news when wunderkind writer Merritt Emmons publishes a breakout book celebrating the queer, feminist history surrounding the "haunted and cursed" Gilded Age institution.