Leading by example has never been Sidney Chambers’ forte.

The vicar with a penchant for crime solving swigged a whole bottle of whiskey before holding a newborn baby in the Grantchester Christmas special, so it’s no surprise to see him swinging forbidden love Amanda around a dance floor shortly after promising his new boss Archdeacon Gabriel Atubo (we still can't believe it's former EastEnder Gary Beadle) that he’ll put duty above his own needs.

Duty is the buzzword in the third series of the ITV drama, and it’s something both Sidney (James Norton) and Geordie (Robson Green) are struggling with as we return to the Cambridgeshire village.

Sidney’s all but shacked up with Amanda Hopkins (Morven Christie), the childhood sweetheart who broke his heart by marrying another fella, only to come running back to the very handsome vicar at the end of series two. 

The bump she was sporting became a baby in the Christmas special, and now both mum and little Grace have become frequent guests chez Chambers, much to the equal delight and chagrin of housekeeper Mrs Maguire.

It’s Sidney’s duty to be a pillar of the community, y’see. He’d be hung, drawn and quartered if anyone knew he was sneaking out for rides with Amanda in the dead of the night. Bike rides, that is, because Sidney is a good man who wouldn’t dream of doing anything improper. No matter how much he and his beloved want to. 

Geordie (Robson), however, doesn’t seem too worried about rocking the boat. The Keating household is anything but happy, and poor Cathy (Kacey Ainsworth) is concerned about her husband’s wandering eye. She has good reason to be, too. Geordie’s got it bad for police secretary Margaret (Seline Hizli), whose quick thinking, wit and intelligence instantly endear her to the detective.

Sidney and Geordie's struggles with their personal duties are put on hold, however, when dead crows start popping up at crime scenes and someone calls up the vicarage to do a spot of heavy breathing over the phone.

The trail leads Sidney back to a funeral he presided over, a young woman nursing her ill father, and a rather depressing institution overseen by Jane Bennett from the BBC version of Pride & Prejudice. No really, Veronica – the woman in charge – is played by Susannah Harker, who you’ll know best as Lizzy Bennett’s older sister in the 1990s smash hit adaptation.

In the process of solving the mystery, Leonard (Al Weaver) jumps at the opportunity to acquire a new friend. His duty, handed down by the new big cheese in his delightfully thick brogue, is to keep his sexuality under wraps. The 1950s sure were fun for everyone, eh?

It’s a big ask for Leonard (who had a heartbreaking series two) but he’s committing to it, sensing an opportunity to find the potential wife his boss recommends. Hilary Franklin, the aforementioned young woman tending to her father, is in real need of a friend, so Leonard kills two birds with one stone (crow joke, har har) and sets himself up to stick his head in the sand.

Sidney, meanwhile, ends up with his head beneath a large quantity of bath water as the mysterious killer decides to take down the vicar via baby Grace. It turns out caretaker Patrick Harland has been seeking revenge for the death of his daughter, Bonnie, at the hands of the folks at that scary institution. His previous victims  – Dr Atwell and Ivy Franklin –were in on the little girl’s drowning and they rather cruelly never revealed what they’d done with her body. 

Sidney and Geordie help him get to the bottom of it eventually, carting off Veronica in a police car and taking Harland to Bonnie’s grave for a somber and long overdue send off, worthy of the children who were wronged by those who were supposed to care for them.

All’s well that ends well, right?  This is Grantchester, of course it’s not.

Sidney and Amanda have had a letter from Guy Hopkins, who’s eager to become a daddy to his abandoned daughter. It doesn’t seem as though Amanda's ex is up to anything too sinister in fairness, but five minutes in his company drives Sidney back to the cigarettes.

“You’re a good man, Chambers,” is Amanda's new motto. But how long can the conflicted cleric keep everyone happy when his demons are knocking at the door?