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What happened? What didn't? Mad Men's most plot-heavy season by far begins with plucky Peggy Olson meeting her new boss, semi-professional philanderer/brilliant ad exec Don Draper — and follows the pair (and their colleagues) through a tumultuous nine-month period of secret trysts, new marriages, heart attacks, business triumphs, and the gradual revelation of Don's big secret: He's really Dick Whitman, a poor prostitute's son who stole his commanding officer's identity during the Korean War. Oh, and at the end of the season, Peggy transitions from secretary to junior copywriter?and gives birth to a surprise baby. Phew!
Essential episode: ''Nixon vs. Kennedy'' — This one is a tough call: Mad Men's pilot is remarkably assured, and the first season finale contains one of the series' most iconic milestone scenes (Don's ''Carousel'' pitch). But it's ''Nixon vs. Kennedy,'' the season's penultimate episode, that best represents what makes Mad Men great — and serves as the season's true climax. A raucous Election Night party pushes Sterling Cooper's office dynamics to the forefront; meanwhile, both Pete Campbell and the audience finally learn the truth about Don Draper's origins. It seems as though our antihero's career (and, perhaps, the show) might be over, until wise old Bert Cooper delivers one of TV's greatest subversions: ''Mr. Campbell, who cares?'' That alone is enough to make this hour a must-see. —Hillary Busis
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What happened? Peggy returned to work, Joan and Roger broke up, and Don and Betty's marriage seemed to be on the mend. But things quickly took a sharp turn when Joan became engaged to an abusive medical student and Don involved himself in another affair, this time with the wife of a client. After being exiled from his home, Don traveled to California met up with Anna (wife of the original Don Draper) while Roger ended his marriage with Mona and accepted a buyout of Cooper Sterling from Putman, Powell and Lowe — without telling Don first. Meanwhile, as Don begged to come home, Betty found out she was pregnant with another child.
Essential episode: ''Meditations in an Emergency'' — Before Don walked out of the firm, before he proposed to Megan, Mad Men gave us one of its most well-constructed season finales. The episode's greatness came not from its storylines, but from the fact that it made you feel as though your investment in these characters' struggles over 13 episodes had been worth it. At its core, the series is about individuals struggling with very public (and very private) demons in a world that is doing the same. In this episode, every character is experiencing their own ''live like there's no tomorrow'' moment, with Peggy telling Pete about his baby and Betty having sex with a stranger at the bar and Don realizing that while he may be selfish, he needs his wife and kids to survive. The decision to merge Sterling Cooper when the entire world could very well have exploded in the next 24 hours was a poignant and gut-punching reminder of the way fear can affect us. We get so caught up in looking for a ''shock'' factor in season finales that we tend to forget what a well-crafted hour can do, and tying the fictional events of the hour to the very real high stakes of the Cuban missile crisis elevated ''Meditations'' to a new level. —Andrea Towers
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What happened? It's 1963, and Don's double life is getting harder to maintain. He's cavorting with Sally's teacher, Miss Farrell, flirting with Conrad Hilton at work, burying one Gene, his father-in-law, and welcoming another, his newborn son. Betty meets a smitten Henry Francis and they find all sorts of reasons to discuss the local reservoir project. At work, Joan prematurely quits to become a surgeon's wife, Peggy and Duck have a fling, Roger's daughter's wedding is ruined by Lee Harvey Oswald, poor Sal gets an unlucky strike, Lois rides a tractor over an exec's foot, and PPL's British emissary Lane Pryce helps the gang strike out on their own. Oh, and Don comes clean. Finally.
Essential episode: ''The Gypsy and the Hobo'' — Contemplating divorce, Betty finally unlocks the secret to Don's past. The moment she confronts him with the contents of his lockbox, ''Don Draper'' deflates before our very eyes. The title refers to the kids' Halloween costumes, and an insipid neighbor gets the last word, asking their uncostumed father, ''And who are you supposed to be?'' —Jeff Labrecque
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What happened? After their divorce, Don and Betty are dealing with the fallout in their own dysfunctional ways. For Don, it's booze and casual sex. For Betty, it's a new husband, an allegedly delinquent daughter (who gets caught masturbating at a friend's house), and problems with the help. On the ad front, Lucky Strike drops Sterling Cooper Draper Pryce, which spurs Don to write an unapproved letter to the New York Times declaring the firm will no longer advertise tobacco. The result? Layoffs and Bert Cooper's resignation. Peggy continues to feel overlooked and checks out the counterculture. Pete is forced to give up a major account to protect Don's true identity and has a baby girl. Speaking of babies...Joan ends up pregnant after a tryst with Roger. The season ends with Don's trip to California to see his friend/the real Don Draper's widow Anna, and the way-too-soon marriage proposal to his young assistant, Megan.
Essential episode: ''The Suitcase'' — This critically praised episode captures the complex dynamics between Don and Peggy while hinting at a deeper relationship. Don forces Peggy to skip her birthday with her boyfriend — who dumps her — to work on the Samsonite campaign. With writer's block looming, they booze it up and openly discuss topics like her secret pregnancy and why they never slept together. After Peggy escorts a completely wasted Don back to the office, they encounter an equally wasted Duck Phillips. Duck calls Peggy a ''whore,'' and he and Don wind up in a sloppy brawl. When the dust settles, Don falls asleep in Peggy's lap and has a vision of Anna Draper holding a suitcase. Among the pivotal moments: Peggy comforting Don as he actually displays raw emotion by sobbing after confirming Anna's passing, and the final scene where Don grabs Peggy's hand as they share a knowing look — about what exactly we don't. —Stephanie Robbins
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What happened? Sterling Cooper Draper Pryce fights to land Jaguar, and Joan makes a major decision in pursuit of the client (hint: it rhymes with ''schmostitution''). Megan leaves advertising to focus on her acting career, which strains her marriage to Don. Betty gains a lot of weight, Sally becomes a woman, Pete has an affair with Rory Gilmore, and an LSD trip ends Roger's marriage. After getting caught embezzling, Lane Pryce hangs himself in his office. And the season ends with the remaining partners expanding the SDCP space.
Essential episode: ''The Other Woman'' — Pete pressures Joan into sleeping with a Jaguar executive to win the car account. In exchange for her, ahem, services, Joan wants to be a full partner in the firm. Don chivalrously tries to stop Joan, but he — and the audience — doesn't realize it's too late. And Peggy, who spent the entire season being mistreated by her mentor, resigns from SCDP to take a job with Don's nemesis Ted Chaough, making Don realize he took her for granted. —Denise Warner
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What happened? The slow burn of the sixth season follows Don's descent into the bottom of a liquor bottle, which rocks his marriage and his career. Meanwhile, SDCP merges with Cutler, Gleason and Chaough to go after Chevy, reuniting Peggy with her former colleagues. All leading to Don's biggest meltdown yet.
Essential episode: ''In Care Of'' — Don's downward spiral into alcohol hits an all time low in a disastrous pitch meeting where he tells a client about his upbringing in a brothel, forcing the other partners to put him on leave. Ted and Peggy's one-night stand prompts Ted to move his family to California and away from her. A brokenhearted Peggy, though, can console herself in her new pantsuit and office — as she is left in charge of creative in the wake of Don's departure. —Denise Warner