Noah Hawley’s newest TV series, a major triumph of the 2017 TV year, presents its second episode. It’ll clarify many of the mysterious elements of last week’s stunningly dense, visually dazzling premiere, but also adds more mysteries of its own. And some more characters, including a deeper understanding of Melanie (Jean Smart), who in tonight’s episode tries to guide David (Dan Stevens) into a detailed reevaluation of his past.