Let's get a few things out of the way: Yay, Joan! Yay, Dawn! Now, what is happening to Peggy?
Peggy suffered a serious personal indignity at the hands of Ted Chaough at the end of last season, and in this year's premiere Lou Avery wasn't making life easy for her professionally. Now Peggy, who over the course of the series has fought so hard for so much, is breaking down.
It's clear at the beginning of the episode that Peggy is being taunted by her peers for her work ethic. They demonize her as a nasty, lonely spinster. "She has plans, look at her calendar. February 14: masturbate gloomily," Ginsberg quips after Peggy asks Stan to do work not realizing it's Valentine's Day. When she sees gorgeous roses on her secretary's desk and assumes they are for her, Stan says: "Hard to believe your cat has the money."
Peggy has gotten to her position by being the woman who doesn't care about Valentine's Day or flowers, so when she thinks the flowers are some desperate act on the part of Ted, she seems to relish in the chance to tell him off. Her protests, however, fall on deaf ears, considering the flowers weren't from Ted. They were a gift to her secretary, Shirley. When Peggy discovers the truth about the flowers, she lashes out at the innocent woman. She's vicious. "You have a ring on," she says. "We all know that you're engaged. You did not have to embarrass me. Grow up." She goes into her office grimacing, facing the humiliation of Ted's heartbreak, the humiliation of Shirley's revelation, and the humiliation of her own over-the-top reaction.
She orders Joan to employ Shirley elsewhere. Unwilling to tell Joan the truth about the flowers, she blames Shirley for the fact that she didn't get work done, allowing herself to become the stereotype Ginsberg and Stan pin her as.
Peggy, in her struggles to get to the top of her field, hasn't had much consideration for the other women around her. Before learning the truth behind the flowers, she says that she should have bought Shirley flowers herself as a denunciation of the holiday. It rings false. Last season, she was quick to scold Joan's initiative when Joan enlisted her to help land Avon. Now, after she once again takes Joan for granted, Peggy is left frustrated and alienated as Joan moves on up in the world. She is the only woman who ends the episode on a downward spiral.
Thanks to Jim Cutler, Joan gets an upstairs office, passing her administrative duties off to Don's secretary Dawn. Dawn's promotion comes after considerable mistreatment from Lou Avery (who wants her off his desk after Sally appears at his door looking for Don and Dawn seems far more concerned with alerting Mr. Draper than attending to his own needs) and Bert Cooper (who's unhappy with her working reception because of his racism). Dawn cracks a satisfied smile as she sets herself up in her new office. Shirley, going to work for Lou, looks content to be rid of her former boss.
Peggy's glass-ceiling-breaking ambition and her unwillingness to take crap from the men around her is her character's greatest virtue. But it has also, at times, made her blind to people enduring similar hardships. She is singular-minded to a fault. This is a woman, after all, who convinced herself she wasn't pregnant and then gave birth. That is not an excuse for her behavior in this episode, but for someone who has allowed herself to be conned by her own psyche in such a way, there must be a particular sort of sting when she learns she has fooled herself once again.