Last night’s episode of Mad Men was appropriately titled “The Monolith.” If you watched, you are likely able to think up numerous reasons as to why this title is a perfect fit, but the aha moment came when Don’s face turned to absolute stone after Peggy informed him he would be working under her on a new account. But even though Peggy took on the task of being a boss, she wasn’t exactly dressed like one. “For that scene, I really wanted Peggy to seem almost like a schoolgirl,” Mad Men costume designer Janie Bryant exclusively tells Instyle.com. “I loved the sailor collar, the dropped waist, the pleated skirt. It’s was a very school girl deal.”

Peggy’s style may come as a surprise since Bryant tends to consistently dress Peggy as a very professional woman—but that wasn’t the only style change in last night’s episode. Roger Sterling and his wife Mona traveled to upstate New York to fetch their daughter Margaret, who had decided to move up there to live in a commune. To paint the picture: “These people are lost and on drugs and have venereal diseases,” says a disappointed Mona, who is desperate to get her daughter back to New York City to raise her young son, of the farm-like commune. So what was it like to costume that scene? “I did so much research on the period and the lifestyle of a commune during that period” Bryant tells us. “I really wanted it to seem other worldly and so separated from the whole uptight, very clean world of the typical Mad Men design,” she adds.

To check out the commune scene (complete with a blend of hippie style and Mona’s New York City fashion), Joan’s standout pink look, and more, browse through the gallery.