While a lot has changed in the world of Sterling Cooper Draper Pryce (Don has married Megan, Joan has had her baby, the civil rights movement is in full swing, Peggy can do the twist, Harry Crane has lost a ton of weight), very little has altered when it comes to the actual characters involved.
Roger Sterling is still a wise-cracking, chain-smoking sleaze. Peggy is still unsatisfied and unrelenting in her quest to get to the top. Pete is slowly achieving his dream of getting everything Don ever had, but he's still not happy because his office isn't big enough. Lane is desperate and alone and Joan is still holding everything together, despite being in the early weeks of motherhood.
And Don? Well Don is still Don. A huge ball of contradictions and confusion. Except he's got the extra addition of new wife, sexpot and 'Zou Bisou Bisou' singer Megan.
Mad Men is always dominated by power dynamics on the big and small scale. Whether it's a civil rights march of Madison Avenue or Roger and Peter squabbling over who has the biggest office, the passing of the time, the battle between youth and experience and the slow evolution of society's values creates a dividing line between the characters.
The power dynamic between Don and Megan is a new layer in Matthew Weiner's world, which looks likely to dominate season five. His former secretary on the surface appears to have all that she wants. Don has moved her into the creative team, they leave and arrive in the office as they please and by the look of their new apartment, he's content to keep buying her affection.
However, the shock and surprise that many felt about Don and Megan's engagement hasn't been brushed under the carpet. The darker side of their relationship was exposed in creepy fashion as Don got turned on by Megan's 'naughty cleaner' act. And of course, there was the surprise party.
Megan's 40th birthday celebrations for Don highlighted the differences between his first and second wives on the show. Betty was the epitome of restraint and (at least on the surface) the perfect '50s housewife. Megan represents the swinging '60s, flaunting her sexuality, extroverted and out for a good time.
The new generation cavorted and partied. Don and Roger looked on with a mixture of embarrassment and bewilderment. Both men appreciate the arrival of change (especially when it involves saucy women dancing in very little clothing), but with their dour suits and whiskey, they very much belong to an old world.
How Betty will slot into Don's new life was an intriguing question mark hanging over the episode. She was mentioned twice by Don during the episode (once with a reference to The Addams Family) and her presence was always felt, even if January Jones's cold-hard stare was nowhere to be seen.
Whether the new world of Megan, Pete, a potential new black secretary and Peggy can actually wrestle power away from Don and Roger will dominate the fifth run. It feels as though it should be an inevitable part of the Mad Men journey, but whether the new world is actually any better than the old (isn't Pete just a more irritating version of Don?) remains unclear.
In Mad Men there is never one storyline going on when you can have 15. Joan and Lane also took centre stage for much of the double-bill, with the arrival of Joan's baby and Lane's increasingly bizarre behaviour towards women giving Jared Harris and Christina Hendricks plenty to get their teeth into.
Mad Men isn't just a show about Don Draper. It's a whole world, which unravels and reveals glimpses of itself episode by episode. No character is wasted. Every detail from the music to the costumes to the brylcreem is perfect. No line or passing look in the office hasn't been thought through and considered.
On this sort of form, it's hard to dispute the argument that this is one of the greatest (if not the greatest) TV shows in the world right now.
Mad Men continues on AMC on Sunday nights in the US and on Sky Atlantic every Tuesday in the UK.
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