Orange Is the New Black Netflix

One of the virtues of this series, whose strong fourth season is available on Netflix, is its sprawling cast. There are the more central stars, including Taylor Schilling, Kate Mulgrew, Laura Prepon, Uzo Aduba, and Danielle Brooks, and then there are the many second tier performers, one of whom, Lori Petty, killed it this season.

Petty plays Lolly Whitehill, the delusional woman with the short bleached hair and the giant black glasses. When she first showed up on the series in season 2, and became a regular in season 3, Lolly was a somewhat endearing, somewhat irritating presence, with Petty employing some actorly tics to make her quirky.

But in episode 7 of season 4, which explores Lolly’s back story, she becomes a far more tragic and believable character, and Petty’s stuttering speaking voice makes a lot of sense. Once we hear the voices in her head, we hear why she talks so fast and so indirectly. Suddenly, a character who seemed to be almost comic relief became one of the show’s most heartbreaking souls. It’s one of TV’s better renderings of mental illness.

In the flashbacks, we see Lolly — for a few scenes played with remarkable similarities to Petty by Christina Brucato — as a promising young journalist in Seattle whose mental illness takes over. Her conspiracy theories get the better of her. She winds up on the street, where she sells coffee and quiets her inner demons by shaking bells at her ears. Alas, she tangles with cops, and winds up in jail. Because that’s where people with mental illness belong?

By the end of the hour, Petty, along with the writers, has brought us inside Lolly’s thinking. It’s a remarkable feat. Petty has been around for a long time; I remember her in “A League of Their Own.’’ I sure hope she makes it back for season 5.

Matthew Gilbert can be reached at gilbert@globe.com. Follow him on Twitter @MatthewGilbert.