The season-to-season differences show up in the small details of its attendant culture. For the fourth season, one of those significant differences is the music. In its first three seasons, Mad Men is populated by the sounds of Percy Faith, Jack Jones, Perry Como, Ann Margaret, Julie London and Brenda Lee, among others. Throughout the series, Matt Weiner and Alexandra Patsavas, Mad Men‘s music supervisor, have chosen recordings that audiences immediately recognize as suitable and relevant to the program’s early 1960s setting. Each record and artist is deployed in a manner that reminds us that a Skeeter Davis record could deliver its fair share of critical commentary. What season four has witnessed is the substantial arrival of rock and roll. Note, not the arrival of a hypermasculinized rock, but a more nuanced version that is both fun and critical. It is a version that is sexy but doesn’t necessitate sex; global yet still somehow American. It is the British Invasion, it is Warhol’s Velvet Underground, and it is radically life changing. Rock in this context is not your parents’ music. Rather it is what hip hop is today: at worst your parents hated and at best put up with it. If you were lucky, they chose the latter because to deny you its place in your life would simply be too traumatic.

And it is here where we cue little Sally Draper’s Beatle-inspired scream from episode ten, “Hands and Knees”. While earlier this season we witnessed that Sally’s discovery of some of her sexuality as she watches The Man from U.N.C.L.E., her entry into adolescence will no doubt be cemented by a Fab Four concert as she is chaperoned by her father. Although Don dismisses Sally ‘s efforts to live with him (and thereby distance herself from Betty) in the previous episode, “The Beautiful Girls”, Sally is temporarily welcomed into Don’s New York life with the promise of Beatles tickets. As Don asked, “Can you keep a secret? You think your friends are going to be jealous when they find out that you are going to see the Beatles this Sunday at Shea Stadium?”, I wondered aloud if Don fully understood what this act would mean to Sally. That remains to be seen.

What is clear is that the British invasion of Sterling Cooper at the end of season two has resulted in a noticeably different firm and a noticeably different direction to the series. This has also meant moments of audible change. For example, the decidedly garage-rock, blues-based sounds of Britain’s The Nashville Teens are featured at the end of the fourth season’s first episode “Public Relations”. Both a nod to Draper’s rural past as Dick Whitman and the lie that Whitman/Draper uses to define himself to reporters at the beginning and end of the episode, “Tobacco Road” is positioned at the episodes end credits as a simultaneously raw and mocking counterpoint. We hear a similar use of pop music at the end the latest episode with Santo & Johnny’s late-1964 release of their instrumental version of The Beatles, “Do you want to know a secret?”. Most famous for their single, “Sleep Walk”, the duo’s instrumental take is neither rock nor roll, nor pop. Accompanied by woodwinds, the duo’s signature pedal steel arrangement is sweet and easy, stripped of any of The Beatles suggestions of intimacy. If George Harrison’s vocals promised a lover’s trust, Santo & Johnny promise nothing of the sort. In fact, Santo & Johnny’s version of the Beatles song, as well-executed as it is, is as excessive in its sweetness as the episode is in secrets.

About Don Draper’s question, “Can you keep a secret?” It is answered repeatedly throughout “Hands & Knees” with a, “yes, but I’d rather not”. Worse yet, those adhering to Draper’s and the firm’s desire to remain quiet are all too often Mad Men‘s women. One has to wonder just how much longer Joan can keep her composure given her most recent trauma and the fact that she is devoted to a distant husband and Roger Sterling’s reputation. Indeed, Roger, Don, and Lane’s secrets have simply become uncontainable and begun to erupt as accounts, identities and loves are lost. Even Pete Campbell cannot escape the fury of hidden truths as he complains to his wife about the plethora of office secrets that swirl about in “Hands & Knees”. Pete’s substantial hypocrisy (see season one affair with Peggy) is rewarded with him being forced to take a symbolic fall to protect Don Draper’s, and by proxy the firm’s, most substantial lie.

Yet as their cynicism and duplicity threaten most of the firm’s partners (I love how Bertram Cooper somehow seems to operate above the fray), I find hope in Peggy and Sally. As celebrated as Jon Hamm is for his work as Don Draper, he has nothing on Kiernan Shipka, whose portrayal of Sally will no doubt go down as one of the greatest acting jobs by a child actor on television in the history of the medium. While Peggy’s complexity has been a mainstay over the length of the show, Sally has emerged as her own person and she is anything but satisfied. The same is true of Peggy whose nascent feminism pops up in a conversation with a would-be suitor who disparages her plight by claiming that there is no comparison between a women’s struggle with those of African-American citizens. Peggy rejects this poet but continues to associate herself with an emerging counterculture. While Draper toyed with Greenwich Village beats in the first two seasons, they were always his exotica. This new rock and roll counterculture, on the other hand, is Peggy’s, and soon-to-be Sally’s, milieu. Peggy’s newfound friends come with a Warholesque happening in episode four, “The Rejected”. Her “scene” is replete with “Velvet Undergroundesque” background noise as well as a experimental films, gays, lesbians, artists, and writers who refuse to work for ad companies. In other words, anything that rejects straight society.

While Peggy’s encounters are somewhat new for her as an adult, one has to wonder what the Beatle fan Sally Draper will make of her teenage world of rock and roll to come. As the mop tops grow beards and go psychedelic, Sally Draper will change with them. How exactly remains unsure. A child of divorce whose father is a professional liar and whose mother has seemed less-than-motherly throughout season four, Sally will most likely turn to the psychic charms of rock. In a word, Sally remains as good a reason to watch Mad Men as any. Whether or not she will find satisfaction in her search remains to be seen. And I’ll be listening. Hopefully, I will be able to hear a secret or two.

Tim Anderson’s essay on popular music and Mad Men is scheduled to appear in the upcoming collection “Mad Men”: Dream Come True TV, ed. Gary Edgerton (I.B. Tauris) available in late 2010.