Don Draper, saying goodbye to another trusted female colleague on “Mad Men.” (Jordin Althaus/AMC)

Don Draper: “Let’s pretend I’m not responsible for every single good thing that’s ever happened to you. And you tell me the number, or make one up, and I’ll beat it.”

Peggy Olson: “There’s no number.”

Just about everybody in last night’s episode of “Mad Men” had a number. Joan Harris — a single mother who prostituted herself for the sake of the Jaguar account but at least negotiated a higher payout and a non-silent partnership for that prostitution — arrived at a number. Lane Pryce is obsessed with a number, namely that $50,000 that he stole from the company and is determined to keep on the books in the guise of Christmas bonuses. Pete Campbell’s “number” in his ongoing negotiation for some semblance of life satisfaction came in the form of insistence that he rent an apartment in the city, something that wife Trudy is adamantly against. (Keep arguing with her about that, Pete. Pretty soon, you’re going to be saying ”Good night, nobody,” and not just while reading the works of Margaret Wise Brown to your kid.)

But Peggy Olson didn’t have a number. Okay, technically, she did. It was $18,000 for a job as copy chief, a salary immediately bumped up to $19,000 by Ted Chaough, arch rival (and former prank caller) of Don Draper, and partner at Cutler, Gleason and Chaough. But as she said to Don (see above), her decision to — MAJOR SPOILER — leave Sterling Cooper Draper Pryce wasn’t about the money.

It was about doing to Don what Dave Chappelle does to his entire office in this classic “Chappelle’s Show” sketch, beginning at the one-minute mark.

“Hey, Don. I’ve got an announcement to make. Ding ding ding ding ding — I QUIT!”

Look, there are only so many late nights at the office that a woman can tolerate, so many times that her fine ideas can be ignored because of Ginsberg’s unstoppable brilliance, so many laxative campaigns a person can work on while watching everyone else happily dig into catered lobster, before she decides it’s time to move on. But more than that, there were only so many situations in which Don Draper could make Peggy Olson feel like a peon before she decided to take control of her destiny. At this stage in her career, Don is never going to see her as anything other than his inferior, that girl who used to be a secretary but is now a talented copywriter only because of Don’s generosity and mentorship, even though she alone just saved the Chevalier Blanc campaign by pulling a Lady Godiva reference out of the curls in her flip ‘do. (Interesting that the term chevalier blanc also can be interpreted as “white knight,” something Peggy clearly doesn’t need at this point.)

So, with encouragement from Freddy Rumsen (Freddy!), a copywriter who was frequently on her side when he wasn’t playing Mozart with his pants zipper, Peggy took the plunge and another offer.

And that gave us one the most emotional scenes of this season so far: watching Peggy tell Don she’s leaving him and his firm. They don’t give out Emmys for Best Reaction to a Piece of Surprising and Incredibly Irritating Piece of Information. But if they did, Jon Hamm would easily win for the 87 expressions that flashed across his face when Peggy said she was going to Cutler, Gleason and Chaough. When he sharply inhaled, I thought he might suck the coffee table, his mod lamps and his mini-bar right down his throat.

Elisabeth Moss was exceptional here, too. She didn’t cry earlier in the episode, when Don dismissively threw a bunch of cash in her face after she insisted that she should work on the Chevalier Blanc campaign instead of Ginsberg. But when it became clear that she and Don were past negotiating, that there was indeed no number he could throw at her to make her stay, and he held her hand in a way he hadn’t since they bonded over the Samsonite campaign, she lost it. The camera angle — which made Peggy appear to tower over Don — and the way Don kissed her hand like a supplicant made it clear who now owned the power in this relationship. Peggy Olson, one-time receptionist (correction: Don’s secretary), had finally done it: she had become better at the ad game than Don Draper himself.

But was it a good move for Peggy to leave? I think it was from a confidence-building perspective. But, like Don, I do not trust Chaough at all. I think he’s far more interested in sticking it to Don than he is in Peggy’s talents.

Then again, if Peggy really gets to shine in her new position, as Freddy suggested she will, maybe she can finally bring over former failed Chaough recruit Pete Campbell. Given the unspoken bond that developed between those two back in season one, it would be fitting if they broke off from the old men who molded them and started competing with them for business.

Also, I would not be surprised if Freddy winds up at Sterling Cooper Draper Pryce, where he would presumably occupy the office Peggy once possessed (remember, once upon a time, she claimed his workspace?) and where, also presumably, he would do his job this time without urinating on himself.

Whatever the future may bring, it was satisfying to see our two key “Mad Men” heroines, Peggy and Joan, moving up in the world during last night’s episode, although clearly the circumstances in Joan’s case were as far from ideal as they get.

Was it just me, or did her evening with Herb the sleazebag remind you of that “Moulin Rouge” scene where Nicole Kidman spends the night with the Duke, only in Joan’s case it involved no operatic Police cover songs, the musicality of Don’s Jaguar pitch (“Oh, this car. This thing”) and a far cheaper neckace?

If Joan had known that Don disapproved of the arrangement, would she have still gone through with it? The “Rashomon”-style telling of that part of the story — the second “Rashomon”-esque narrative of season five — suggests she would not, perhaps in part because of the negative impact it would have on Don’s view of her. (“Who wants to be in business with people like that?” said the suddenly moral Don. Uh, newsflash, Don: you and your associates took a client to a brothel six episodes ago. Joan is already in business with people like that.) Despite what many commenters said after last week’s recap, I still think Joan has some genuine feelings for Don. And I also still believe that before this series ends, Don will indeed attempt to hit that.

Ultimately, Joan is a practical woman. And as much as it pains her and makes her feel small inside, she knows that her biggest asset in the eyes of everyone else is... well, her assets.

So she finally got a powerful position in the office, by using what’s always gotten her somewhere in this world: her body. And by doing so, maybe she’ll finally be able to exercise her mind, or at least put her kid through college. The means? Horrendous and certainly not worth pursuing from a moral perspective. But the ends? Maybe they could be good for our Joanie.

And Peggy finally got some satisfaction by using what’s always gotten her somewhere: her brain and her calculating business sense, the latter of which she developed courtesy of Mr. Don Draper.