Call the Midwife, now in its fourth season on PBS, must be one of the most conflicted series on television. On the one hand, it's an exceedingly comforting feeling to return to Nonnatus House and catch up with our lovely midwives. But that cozy feeling is soon punctuated by the screams of mothers in labor, and the high-pitched squeals of their newborns. Duty calls!

Though the show's source material was exhausted by the close of the second season, Heidi Thomas and her team of writers have found plenty of new ways to explore all aspects of maternity and motherhood in Poplar, while still keeping the stories feeling true to the real experiences of Jennifer Worth, or "Jenny Lee" on the show (who, though her character version has left us, is still narrating each episode thanks to Vanessa Redgrave's soothing, framing overtones).

Nonnatus House, though, feels somewhat scattered these days. After Jessica Raine's departure and Bryony Hannah's character Cynthia leaving to become a nun (she does return halfway through the season), only Trixie (Helen George) is left as the only anchor from the old days. She's also busy with her curate beau, Tom (Jack Ashton), and dealing with some internal demons, while Patsy (Emerald Fennell) has a budding relationship of her own -- though it's one that she must keep quiet. The girls are joined this year by another new midwife, Barbara Gilbert (Charlotte Ritchie), a plucky and tirelessly devoted nurse who -- like Patsy in her first season -- hasn't gotten much of a story of her own yet, which means she takes over a lot of the midwifing plots (the same is true of Victoria Yeates' Sister Winifred).

The elder sisters of the house are also facing new changes and challenges of their own. Sister Evangelina (Pam Ferris) must confront the truth of her age slowing her down, while Sister Monica Joan (Judy Parfitt) gets a boost in confidence after she's forced to assist in a birth. The sisters (still more than ably lead by Jenny Agutter's Sister Julienne) also take on another midwife their age, Phyllis Crane (played by the great Linda Bassett), who gives Sister Evangelina a run for the award of Most Crotchety.

Bassett joining the series brings to mind another sweet and comforting PBS series in which she starred, Lark Rise to Candleford. But things are actually beginning to feel darker in this season of Call the Midwife, which begins in 1960 with a story of the abuse and neglect of four young children of Poplar. The show has never shied away from portraying the poverty and desperate surroundings of East London, and several storylines these year focus specifically on the way things are changing. Winifred starts a campaign to educate prostitutes -- many of whom already have syphilis -- about the values of safe sex; Dr. Spock comes on the scene; and issues of women's rights are broached in several different ways. Not all of these changes are triumphant, though, like when women are starting to get treatment via the new "wonder drug" thalidomide.

The wonderful thing about Call the Midwife, though, is that no matter how complicated the pregnancy, or how much a father wants a son instead of a daughter, or how dire the situation surrounding the mother-to-be and her babies, things tend to wrap up in a plausibly content fashion. Not always, but often. Most comforting of all, despite the screams of pain and calls for Doctor Turner (Stephen McGann) no one ever dies in childbirth.

Still, there are other pains, and other true joys. One thing Call the Midwife understands -- that so many other shows simply don't -- is that drama can come from joy and happiness, and not always from violence and death. Season 4 is no different than any other in that regard. Occasionally, an episode that will have been drifting along steadily in a mire of afterbirth and jazz records will suddenly overwhelm all of your emotions. The show is never saccharine or manipulative, it just tells great stories in a fully-realized world. And, often, the culmination of its tales is truly beautiful. Despite any other gruesome moments or graphically-portrayed issues surrounding poverty and childbirth, that, at least, is a comforting thing.

Rating: ★★★★ Very good — Damn fine television

Call the Midwife Season 4 premieres Sunday, March 29th at 8 p.m. on PBS

The series also stars Miranda Hart, Ben Caplan, Laura Main and Max Macmillan, in its sprawling cast -- all of whom are back and active around Nonnatus House in Season 4.