BY all accounts, Tatum T. Bass seemed like the quintessential Miss Porter’s girl. She was pretty, popular and athletic, running track for the school even before track became an official school sport. She had good grades and consistently made the honor roll.

Then, somewhere along the line, everything unraveled. By her own admission, she skipped classes and cheated on an art history test. And while the school cited those transgressions when it expelled Miss Bass in November, her side of the story is much darker: in a lawsuit against Miss Porter’s, Miss Bass says she was driven to a nervous breakdown by constant harassment from a secret society of girls who call themselves the Oprichniki, taking their nickname from a 16th-century Russian torture squad.

Although students are often expelled from elite boarding schools, seldom do they sue. And while neither she nor the school will discuss the case, her complaint offers a tantalizing window into a world that has been glamorized and vilified by everything from “The Official Preppy Handbook” to “Gossip Girl.”

As two pictures emerge in this case, the question is: how much of this world really existed? Parts of Miss Bass’s story seem fairly straightforward. In the fall of 2005, she left her parents’ home for Farmington, Conn., and the bucolic campus of Miss Porter’s, an all-girls boarding school best known for its roster of illustrious graduates: Jacqueline Kennedy Onassis, Gloria Vanderbilt, Dorothy Walker Bush and many others.