Season 5, Episode 5

It’s a big week for Sierra. Played by Emily Browning, this new-agey daughter of Hollywood royalty — and the mother of a son with Helen’s dead partner, Vik — joined the slim ranks of non-core characters who have gotten their own point-of-view segments. In that segment, she lands the title role in a hot director’s adaptation of “Madame Bovary.” (She lands the director, too.) She receives a visit from her movie star mom. And she nearly kills herself and her infant son in a coked-up car crash.

As one might expect, these events are not unrelated.

Jennifer Jason Leigh guest stars as Adeline, Sierra’s mostly neglectful, very famous mother. Fresh from a jaunt to Nepal, she shows up expecting to easily reinsert herself back into Sierra’s life, whether by babysitting her new grandson (whose age she doesn’t know) or by “helping” Sierra rehearse a scene.

As hard as it is for Sierra to endure Adeline’s narcissism, it’s even harder to fight against it. Faced with the slightest pushback — Sierra very mildly shades her mom for dragging her from set to set as a child until her father stepped in and made sure she attended school — Adeline withdraws completely and pointedly, reneging on her babysitting commitment as a passive-aggressive punishment.

It’s rare for “The Affair” to dump a full-fledged heel like Adeline on its audience, and for good reason. The show’s characters have always thrived on nuance, contrast, even contradiction — characteristics that render clear-cut heroes and villains obsolete. That’s what makes Adeline a misfire, even in the hands of an actor as gifted as Leigh. Debuting as she does in Sierra’s first P.O.V. segment, before we’ve had a chance to see much of the world through her daughter’s eyes, she comes across as a grinning, oblivious monster. She’s a one-note character, and that one note nearly drowns out this entire section of the episode.