Personally, I'm tempted to think he might end it all in a car crash of ambiguous cause, while drunk, after discovering he is dying from lung cancer. There'd​ be a certain brutal poetry in that – taken out by the holy trinity of advertising accounts, the automobile, alcohol and tobacco – but it wouldn't be pretty. And if there's one thing Mad Men has consistently been it's pretty. Even – maybe especially – when its characters are behaving ugly.

So Don (Jon Hamm) probably won't die on the road, but that doesn't mean Mad Men can't throw in the odd Kerouac reference anyway. There's Don striking out on a seven-hour car trip to Racine​, Wisconsin, on the trail of Diana, the hunted and haunted waitress (Elizabeth Reaser​). And there in the passenger seat is the ghost of Bert Cooper (Robert Morse).

"Riding the rails," Ghostbert​ says. "Maybe to some waitress who doesn't care about you? You shouldn't do that."

"It's not going to stop me," Don says.

His sudden trip is spurred by a moment of … what would you call it? Ennui? Recognition? Horror? Whatever it is, it feels like a tipping point for Don. Not the first, but given how little fuel there is left in this tank, it's quite possibly the last.

He's in a boardroom presentation at his new home, McCann Erickson, where the wind whistles through the window of his sky-high eyrie-cum-prison cell. The client is Miller beer, and this is supposed to be the moment he's dreamt of all these years. Finally, a beer brand. Better yet, a new beer brand. He can build it from the ground up. This is it, surely.

That's certainly how it feels to Jim Hobart (H. Richard Greene), the evil mastermind who has brought the whole Sterling Cooper & Partners crew into the fold – a manoeuvre that was all about getting Don, really.

"We just bought an entire agency in Milwaukee to get Miller beer," he tells him, and as a pick-up line it's hard to beat.

"For me?" says Don coyly.

"When I want something I get it," says Hobart. "And I've been trying to get you for 10 years. You're my white whale, Don."

A minute later, Hobart asks him to try his new signature, using his married name.

"Have you said it yet?"

"What?"

"Have you introduced yourself?"

The camera zooms in on Don. "I'm Don Draper," he says, throwing his arms wide in that graceful, charming salesman way he has. "From McCann Erickson."

Hobart clutches his heart.

But in that boardroom, Don is like Betty was in their marriage. Confronted with the prospect of having it all, "it all" suddenly seems startlingly empty.

The guy at the head of the table is presenting research on beer drinkers, but he tells them he doesn't want this to be about research, it's about a man. He's in full storyteller mode, like Don Draper only without any of the warmth or emotional connection with the tale he's telling, or with his audience. He's like an A-I that has all the data but can't yet simulate the things that make a human human.

As everyone in the room flips the pages – the researchbot​ is clearly reading from a script – Don turns his back on this failed Turing test. It's like he's witnessed the magic he does reduced to a mechanical echo; or maybe it's that he's seen himself replicated; or perhaps he's just seen himself.

Whatever, he doesn't like it.

It's horrifying, in fact. He needs to get out. A plane flies across the sky, its vapour trail streaking across the rear of the Empire State Building on the Manhattan skyline, and that's his signal. He's gone.

Joan, meanwhile, is determined to stay. It's great how much this season has been about her battle to be taken seriously, and appalling how much the deck is stacked against her.

One of the McCann A-holes from that panty​ pitch a few episodes back is in her office "helping" her say hello to the clients she has spent years developing relationships with. He butts in on her, repeatedly, while she's talking to the Avon guy. He tells the guy he's heading his way, they should play some golf. "Are you any good at golf?'

Awkward pause.

"No, I'm not."

The call ends and Joan is horrified. "I don't know what to say except Barry is in a wheelchair."

She'd given this jerk briefing notes on all the clients, only he hadn't bothered to read them. His response on being called out? "Who told you you get to be pissed off? I thought you were going to be fun."

Which, it turns out, is how everyone imagined she would be. Which, it turns out, is code for an easy lay.

When Joan complains to Ferg Donnelly (Paul Johansson​) that Dennis isn't working out, he seems at first to be unsympathetic.

"Here's how it looks," he tells her. "Like some junior account man came in and started swinging her elbows."

"He didn't read the brief," Joan protests, skipping right over that "account man" bit. "And I'm not Dennis's junior."

"Joan. See it from his side. He has a wife and three children. He's not going to work for a girl. What's he going to say to the client – 'she's my boss?'"

Just as Joan is about to hop on the high horse of righteous indignation, Ferg​ offers a sop.

"You'll certainly get the respect you desire now it's just you and me," he says.

That's good news, but Joan's relief evaporates faster than the alcohol in the whiskey he has just poured when he adds: "It would be good to get out of town ... I'm not expecting anything more than a good time. I want to get to know you, of course."

Joan is rapidly running out of places to take this; above Ferg​ there's only Jim Hobart, and he really doesn't want to know.

"It may not have sunk in," he tells Joan, "but your status has changed. I don't care about your SC & P partnership. I don't know if someone left it to you in their will but your little stake doesn't mean anything here."

Joan threatens to make it a legal issue, raises the spectre of Betty Friedan​ leading a phalanx of angry feminists up Fifth Avenue to the McCann doorstep. Hobart backtracks, offers her 50 cents in the dollar on the half-million still outstanding on their deal, but Joan is playing tough – so tough she risks losing it all.

"I guess I wasn't clear," she says. "I'm not negotiating."

"Then go ahead," Hobart says, his eyes gleaming with barely suppressed rage. "I'd rather give it to a lawyer."

In the end, and with Roger's urging and the gentle prodding of her new real estate mogul lover (Bruce Greenwood), Joan does take the settlement. If that's the end of her storyline, it's as frustrating as it is fitting: you wouldn't call it a total defeat, perhaps, but it sure doesn't feel like any kind of victory.

Back on the road, Don turns up at the house of Diana's ex-husband. He charms his way in with some cock-and-bull story about Diana having won a competition, but while the new Mrs Baur falls for it, her husband – Diana's ex – sees straight through the ruse, and the cover-up of the cover-up that follows, when Don claims to be a collections agent chasing debts.

"The suit, the shoes, the Cadillac – you're not in collections," Cliff (Mackenzie Astin​)  tells Don.

He knows what Don is really after. "You think you're the first one that came looking for her? She's a tornado, just leaving a trail of broken bodies behind her."

"I was worried about her," says Don. "She just seemed so lost."

But it's not Diana who's lost. Not really. It's Don. It always has been.

Driving down a country back road, he stops to pick up a hitchhiker. He's heading to St Paul, a long way from Manhattan. Completely the wrong direction, in fact.

"I can go that way."

"I don't want to take you out of your way, man," says the hitcher.

"It's not a problem," Don says, as the end credits roll and David Bowie's Space Oddity kicks in – a song about a man cut adrift in time and space, doomed to die a lonely death in the tin capsule in which he is travelling.

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