Most of what I read about the latest Mad Men ("The Other Woman") focused on Joan's decision to accept Pete's indecent proposal—and rightly so—but the title of the episode basically demands the audience answer the question "Who's the woman, and who's the other one?" As far as I can tell, the consensus seems to be that it's Joan, who unlike Megan and Peggy lacks a defined role in Don's life, but that strikes me as only significant in this episode and inconsonant with developments in the series as whole. Moreover, the final minutes of the episode indicate that while Peggy's role in Don's life may have been circumscribed by their working relationship in recent episodes, it bears remembering that, before Megan, Peggy and Don regularly confided in each other about things like the ramifications of unplanned pregnancies. In short, I'd argue that over the course of five seasons, Peggy's been Don's perpetual "other woman," and I think the structure of the episode bears this out.
But first things first, let me remind you of a moment from the first episode of the first season. Don criticizes Peggy for allowing Pete to enter his office and steal research from his trash, to which Peggy responds thus:
Don removes her hand, criticizing her again for attempting to manipulate him with her feminine wiles, then he comforts her:
From the beginning, Don's seen in Peggy a potential unrelated to notion that woman are sexual objects designed for male consumption—and she's the only female he hasn't fathered that he seems to feel this way about. She's exceptional in that she'll always be "the other woman," the one he doesn't desire for reasons that can't be reduced to the fact that she's not conventionally attractive. Don's occasionally paternal, occasionally fraternal affection for Peggy seems grounded in the recognition that she, like him, doesn't belong in the social circles of the advertising world, as well as it's corollary: that she, like him, can produce better copy because they're of this world instead of in it.
The last five minutes of "The Other Woman" seem to bear this out. Keeping in mind that closing an episode is akin to owning it—the final moments will be the lasting impression left on the audience irrespective of the events they capstone—it stands to reason that for all the attention paid to the means by which Joan attained a partnership, "The Other Woman" belongs to Peggy. The celebration that accompanies landing the Jaguar account—which should, if Joan's actions are the centerpiece of the episode, be front and center—is pushed off-frame as Peggy confronts Don in the hall. Here's Don about to join in the festivities:
When he stops to talk to Peggy, director Phil Abraham cuts right in a manner that eliminates the celebration from the frame:
As the conversation continues, the sequence of shots and reverse-shots diminish the significance of the celebration which now only exists in the diegetic space as background noise. It acquires a status not unlike the act it celebrates: the partners know what Joan did and every time they look at her (or think of Jaguar) the knowledge that they prostituted her will reemerge like half-heard chatter at a party they barely recall attending—not unlike an off-frame celebration represented on-screen by noise leaking through glass walls.
But let me back up: Joan's sacrifice is rendered so insignificant that the celebration of its fruit doesn't merit screen time. Not only doesn't it merit screen time, but even when it should be visible it isn't:
When Abraham reverses back to Don, Peggy's head largely obstructs the audience's view of it. Even if it's partially visible on the right of the frame, it still plays second-fiddle to an unfocused shot of the back of Peggy's head. As the conversation continues, Abraham shifts from these medium shots of Don to medium close-ups of the both of them:
The sounds of celebration can still be heard, but they're distant and indistinct compared to this conversation. The framing alone suggests its thematic significance, but just in case the audience missed it, Abraham moves the conversation to Don's office:
Peggy follows him in and this reminds me of something from that first episode:
Different offices, but Peggy's posture, her position relative to Don and the impersonal scale of the long shot are strikingly similar. Moreover, as in "Smoke Gets in Your Eyes," what begins as a cold sequence between professionals quickly evolves into a series of mutual recognitions. What they recognize has changed—what had been potential in the former has been realized by the latter, such that Peggy's departure now constitutes an actual loss instead of a hypothetical one—but so too has the dynamic between them. As in the first episode, Peggy offers Don her hand:
Only this time he doesn't reject it. He really doesn't reject it:
Whereas in the earlier episode Don clearly dominated the frame, in this one he only appears to. He occupies more space and is afforded frontality—if only by virtue of being the only one in the shot with a head—but his posture's that of a supplicant. The man who once upbraided her for touching his hand in an unprofessional manner is now a partner in a firm that whores out cherished employees for profit. He's kissing the ring because he knows his is now the morally inferior party.
And instead of returning it, Peggy just steps into the elevator:
If Joan can't even own the episode in which she sells herself to make partner, how likely is it that the partnership she entered will work?