The new season of PBS’s delightful murder mystery Grantchester starts off by replenishing a bit of Grantchester’s population.

For a small sleepy village, Grantchester has always had a remarkably high murder rate. That’s been helpful for the premise of the show, though perhaps troubling for the inhabitants.

The third season, which premieres Sunday at 9 p.m. ET, starts with a birth rather than a death. Amanda Kendall (Morven Christie), long-time love of main man Sidney Chambers (James Norton, with Christie, top), is about to deliver the baby with which she became pregnant in season two.

While on balance this is happy news, it does create complications, because sharp-eyed viewers will remember that also last season, Amanda left her husband Guy Hopkins (Tom Austen), the baby’s father.

It had been an arranged marriage, and when he became just too uncaring and indifferent, she decided she didn’t want to live the rest of her life that way.

That decision wouldn’t be news in 2017. In 1954, when Grantchester is set, it was considered wildly radical. 

Amanda was further prodded, not incidentally, by the fact she had always loved Sidney, just as he had always loved her. The fact she had been committed to this arranged marriage had left her frustrated and left him as the pious, sincere and unhappy vicar of the local Anglican church.

Now that Amanda has left Guy and had the baby, whom she names Grace, she and Sidney have come to a different crossroad. Single motherhood was scandalous enough in the mid-1950s without the village hearing that the substitute de facto Dad might be the local priest.

Much of this season’s first episode, which aired in Britain late last year as a Christmas special, shows Sidney and Amanda contemplating their seemingly impossible situation even as they both yearn to live and raise the baby together.

In the broader picture, as this suggests, the baby drama temporarily shifts the traditional focus of Grantchester.

While the show has always shown us the lives of its central characters, who also include Sidney’s crime-solving partner Detective Inspector Geordie Keating (Robson Green, with Norton, right) and Sidney’s grouchy housekeeper Mrs. Maguire (Tessa Peake-Jones), the primary focus of each episode has been solving a murder. 

This episode has a murder, too, which requires Sidney and Geordie to outthink a criminal with the help of several bottles of liquor.

But Amanda’s story becomes the real focal point, especially after her own father – who set up her marriage and considers her bailout an unforgiveable betrayal – literally throws her into the street.

Pregnant lady, Christmas Eve, cold snow everywhere, no room at the inn. Perhaps you’ve heard this story before.

Happily, an unlikely hero steps up to help save the day: Leonard Finch (Al Weaver), the gay, nervous, well-meaning and sometimes annoying curate who works with Sidney

Well played, Leonard.

Acting honors for this episode go to Christie, who conveys how hard Amanda must work to hide her anxiety over the ways her situation could go wrong. At the same time, she’s clearly determined that in the future, no one will run her life for her.

The season’s subsequent six episodes will likely tilt Grantchester back toward its traditional emphasis on murder.  

But baby Grace can’t be unborn, so it’s clear we’ve got a prominent new element in the mix. Instead of drinking because he can never be united with the love of his life, Sidney will now get to drink because the union is on the table and he’s got no good path to closing the deal.

We like Sidney, by the way. And we like Amanda. We really want them to be happy. We just understand that, as people would say 60 years later, it’s complicated.

In any case, the one certainty is that whatever new lives are added to Grantchester, old ones will continue to be snuffed out.