Mad Men took a daring turn at the end of the third season by rebooting itself (the principals at Sterling Cooper left to form their own upstart agency in the face of a corporate takeover), and it pays off big time in season four. Set a year after that season finale, the brand-new agency Sterling Cooper Draper Pryce is struggling to make a name for itself and sign on new clients; Roger (John Slattery) finds himself at the beck and call of the firm's largest account, Lucky Strike; Pete (Vincent Kartheiser) faces impending fatherhood; Peggy (Elisabeth Moss) asserts herself in a position of power among her sexist fellow copywriters; Joan (Christina Hendricks) sees her husband off to Vietnam and finds herself in a compromising predicament. Then there's Don (Jon Hamm, doing his finest acting yet), who brazenly gambles the firm's success on his impulses, lives alone except for a string of one-night stands, and exchanges curt phone calls with his ex-wife, Betty (January Jones), over parenting the kids. Don's rock bottom midway through the season (which hits somewhere around his career high) collides with the shattering loss of a loved one, and his attempts to improve himself include forging a new romance with a confident, intelligent marketing researcher (Cara Buono). But the woman with whom he's most deeply linked--platonically--is Peggy, and the two of them have a terrific episode all to themselves entitled "The Suitcase."