Margaret spends most of season three dealing with the unraveling of her marriage to her husband, Tony, although she has a brief moment of diplomatic triumph on a trip to the US. As their relationship turns mutually destructive and toxic, Margaret learns that even her own family sides with Tony — because he's charming, and she's always been "difficult."
Instead, Margaret seeks refuge in her non-royal friends, and eventually sparks up an affair with a much younger man, Roddy. When news of the affair breaks, the royal family is scandalised, Tony presses his advantage, and, after witnessing a fight between Margaret and Tony, Roddy breaks it off. A despondent Margaret nearly overdoses on sleeping pills, but survives and is last seen encouraging Elizabeth to stand tall and continue to lead.