A suburban housewife discovers her husband of 10 years has been living a lie and is not the man she thought he was. An unwed mother, already at odds with her Catholic upbringing after giving away her baby, embarks on an ill-advised affair with a predatory older former co-worker. A hapless secretary accidentally severs a high-flying executive's foot while riding a motor mower through an open-plan office.

Any of the plotlines above, including that last outlandish one, could have come from EastEnders, Corrie or Neighbours. Even more likely, they could be pivotal events from arguably lower rent daytime American "serial dramas" such as Days Of Our Lives or The Young And The Restless. In actual fact, they all feature in the third season of perhaps the most lauded television show currently in production.

For the last three years, critics have been falling over each other to heap praise on Mad Men, the latest addition to an ever more impressive catalogue of groundbreaking quality television in the mould of The Sopranos (where series creator Matthew Weiner cut his teeth as a writer), The Wire, The West Wing or Six Feet Under. Words like "smart", "cool", "genius", "brilliant", "enthralling", "innovative" and "amazing" adorn box sets of the series, lifted from reams of positive press - but rarely, if at all, will you find any of these superlative-packed tributes employing the word "soap".

Whisper it, for fear of upsetting TV snobs, but Mad Men is a soap, albeit one, in the spirit of the creative campaigns of the programme's fictional Sterling Cooper advertising agency, meticulously dressed up to look like it isn't. It's all in the packaging, of course, the persuasive construction of an illusion, the skill of seducing consumers into buying something they never knew they needed but now realise they can't live without.

George Lois, pioneering ad executive and former staffer at Esquire magazine in 1960s New York, with whom Mad Men's Don Draper shares more than a smidgen of DNA, hits the nail on the head in the introduction to his 2003 book Sellebrity: "When a campaign has the power to become new language and startling imagery that enters the popular culture, advertising communication takes on a dimension that leaves competitive products in the dust." It's that strain of innate media savvy which resulted, four years later, in Weiner selling us the idea of a show about people selling things.

It was Weiner's pilot script for Mad Men, written as far back as 2000, that landed him the writer's gig on The Sopranos, whose head honcho David Chase immediately understood the concept. "It was lively and had something new to say," he told the New York Times on the eve of the show's debut. "Here was someone who had written a story about advertising in the 1960s, and was looking at recent American history through that prism."

Thus, through the 39 episodes of Mad Men that have aired in the UK to date, we see an America going through seismic cultural and political shifts; the rise of the civil rights movement and the attendant importance of capturing the "negro" market, the emergence of pot-smoking turtle-necked beatniks as barometers of taste and attitude, and the birth of politics as a media-driven product. In the 21st century, leaders are routinely victorious thanks to the power of television, but in 1960 a sweaty and awkward Richard Nixon was arguably the first presidential candidate to lose an election via the small screen.

Our own knowledge of the last half-century, and the early 60s in particular, assists Mad Men in establishing its revisionist backdrop, what Chase describes as the show's "prism". When, early in Season Three, the viewer catches a glimpse of the date on Roger Sterling's daughter's wedding invitations, we know well in advance that shocking events in Dallas later that year (1963) will put a downer on the impending nuptials. However, it's a card that Weiner admirably never overplays, because in keeping with all good soaps, this is a show that ultimately thrives or flounders on the strength of its characters.

Don Draper (Jon Hamm), the de facto lead of the piece, is as much a well-honed product as anything Sterling Cooper are charged with selling; a rural hick with an unhappy childhood, he assumes the identity of a dead soldier to reinvent himself and build a new life at the apex of the American dream. Yet beneath the tailored suits and towering confidence, his past and his restlessness gnaw away at the superficiality of his fabricated identity.

His bosses, Roger Sterling (John Slattery) and Bert Cooper (Robert Morse), represent men out of time and place, old hands not best equipped to cope with the escalating pace of the changing world. They're as much obstacles to Draper's progressive attitudes as Draper himself is to his nakedly ambitious but largely untalented underling Pete Campbell (Vincent Kartheiser).

But in contrast to the programme's title, it's the female leads that are tasked with carrying the lion's share of narrative momentum in the third season. When we first met Don's wife Betty (January Jones), she was the epitome of the prim housewife in countless magazine advertising pictorials of the period. Stylish but unfussily dressed, she was the stay-at-home mom and queen of her pristine kitchen, only beginning to unravel and emerge as a proto-feminist icon. The Season One episode where, cigarette between pursed lips and brandishing a shotgun like a suburban Bonnie Parker, she fires off both barrels at a neighbour's pigeons was an early indication that domesticity wasn't necessarily blissful.

Peggy Olson (Elisabeth Moss, previously seen as the president's daughter Zoey in The West Wing) began life as Don's nervous and naive secretary, but by Season Three had bloomed into a smart and intuitive career woman, via leaving home, turning her back on her newborn baby, dabbling in marijuana, going to Bob Dylan concerts, and indulging in afternoon quickies in anonymous hotel rooms. Keep an eye on the dialogue exchanges between her and Don, and see how many of them could just as easily apply to the Drapers themselves.

Joan Harris (Christina Hendricks) may well be the prima Mad Men heroine, despite starting out as a fairly unlikeable bitchy office vamp, ludicrously voluptuous to the point of a living cartoon. A run of bad luck and unfulfilled potential later, she became an audience favourite, the capable troubleshooting earth mother to whom everyone turns when their worlds fall apart. It's no surprise that Hendricks now ranks alongside Hollywood big screen A-listers as an in-demand cover star for high-end glossy magazines, nor that the Mattel doll of her character - noticeably more modestly proportioned than the real thing - out-sells the rest of the range (Don, Betty and Roger) put together.

That's right, there are Mad Men dolls now; a sure sign of a TV show transcending its humble roots and discreet scheduling. The accepted industry parlance for such items is "action figures", but the slowburn nature of the series, its determination to move at its own laconic pace makes the word "action" a curious misnomer. It's a soap with style and substance, where what's not said is equally as important as every line of perfectly-judged dialogue, its makers respectful enough to credit the viewer with the intelligence to fill in the blanks.

In a small screen world where dramatic upheavals and cliffhangers are self-defeatingly revealed in newspapers and magazines for weeks leading up to transmission, and then punctuated by the faux surprise of synthetic drums before the credits roll, the delicacy and subtlety of Mad Men offer a masterclass in persuasion. This is how you tell a story; this is how you sell a soap.

Season Three of Mad Men is out now on Lionsgate DVD and Blu-ray