It all seemed to be coming together for “Big Love.”

After a misfire of a fourth season in 2010, and a fifth season this year whose recovery has been hit-and-miss at best, the March 6 episode produced a scorching final halfhour that held the promise of redeeming the entire show.

In that episode, the issue of cults came up, first with Margene’s willing participation in what has clearly been a pyramid scheme of a business. Moments later, the tables were turned, and Margene confronted her family and the audience with the question of whether lead character Bill Henrickson (Bill Paxton) was himself a cult leader in his unyielding, destructive bid to promote polygamy (“The Principle”) at all costs.

Bill It was stunning, and yet it made so much sense. Bill’s humanity had helped make the first three seasons of “Big Love” so compelling, but since then, he has been so megalomaniacal that he has become loathsome, raising the question of why anyone should be on his side. That March 6 episode raised the possibility that Bill might be headed for his comeuppance in a profound way.

That reckoning day might yet come, but Sunday’s most recent episode, the last one before the March 20 series finale, took all the air out of the balloon. WIthin the first five minutes, the cult storyline was abandoned, as Margene meekly quit working for the Goji Juice company that launched the entire arc. And the rest of the hour continued in the sensationalistic and often nonsensical manner that has plagued “Big Love” the past two years.

How many characters behaved in ridiculous and unsympathetic ways Sunday? Well, there was Bill, Barbara, Nicki, Margene, Ben, Rhonda, Cara Lynn, Alby — a list that pretty much includes all the ones who count. And how many didn’t? Heather, Lois, maybe Frank — all of them minor characters appearing in a scene or two.

There’s one more episode to go, one more chance to salvage a series that once was one of the best on television. Faith in the face of your family’s utter collapse is the lead theme heading into the finale, and perhaps “Big Love” will bring it home in a meaningful way, and not in a way, as many of the characters on the show must feel, that all this suffering has been for naught.