Ah, the Pete episode. It’s the one we’ve been waiting for, and what twisted joy was on offer as Matthew Weiner steered us from the Campbells’ suburban hell of a dinner party, to a Manhattan brothel, to a fist fight in the boardroom. Pete, as Lane Pryce observes just before he challenges the young pretender to a scrap, has become a monster of late, drunk on power. Roger and Lane, the ageing partners, feel it most acutely and they've both perfected that look: the one that says, with a twinge of sadness, who the hell does this punk think he is, and when did I get so old? Pete’s scorn has become his trademark, but it’s fuelled by desperation. He’s hungry for recognition, for success, for the sexual attention of a teenage girl he meets at a driving safety lecture – but more than anything he’s desperate for Don, for his friendship and approval. Pete’s tears in the lift, spilling out of his quickly blackening eyes, are the tears of a child exhausted by humiliation.

Friendship threads through the episode – Don’s lack (Megan points out that she was forced to invite his accountant to his birthday party); the revelation of a pact between Ken and Peggy, that if one leaves the firm the other goes with them; Joan carrying a bucket of ice into Lane’s office post-fight (only for him to ruin their moment of solidarity by lunging like a fool). All these little alliances and kindnesses fill in the sad picture of Pete’s isolation. He is lost in the suburbs, his wife enamoured by a new baby, and he is friendless at work, where everyone who he’d call a friend loathes him. He consoles himself by role-playing with a prostitute (she gets it right when she calls him a king), and trying to seduce a teenager – all ways of pretending to be the alpha male he wishes he was. But neither works: he is furious with drunken shame after the brothel visit (where Don abstained) and watches helpless and humiliated as the teen falls for a kid her own age (called Handsome).

Poor Pete. That Weiner can retain our sympathy for a character so slippery and loathsome is testament to his writing, and the skill of the actor, Vincent Cartheiser. In the first series, I remember finding the performance absurd, false and posturing. But Pete’s unravelling, in the hands of Cartheiser, has been slower and subtler than most, and his scenes of true revelation – the agonising meeting with his father, or when Peggy tells him about their baby – show the tenderness beneath all that tortured swagger.

And oh, what a fight. There have been a few punches, or near-punches, in Mad Men – Don thumping Jimmy Barrett, Don trying and failing to thump Duck – but I don’t think there has been a fight quite as agonisingly prolonged and hilarious as that between Lane and Pete: two skinny men with their fists raised, making sure their ties are out of the way, rocking on their feet in their smart office shoes. It’s undignified, and a great comic skewering of macho business culture (listened to, disbelievingly, by Joan and Peggy through a wall). You watch Mad Men for scenes like this: high drama, an element of farce, a sense of something fundamentally shifting beneath the surface. Saying that, there are still scenes which seem a little overstated – did Don really have to rip off his shirt to tackle Pete’s broken kitchen sink in a Superman frenzy of manliness as Pete rifled forlornly through his toolbox? We get it: Don’s still got it, and Pete, poor Pete, is a shadow of a man, grasping at a life.

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