The times they are a changing in the ITV drama: rapidly approaching the swinging 60s, the new episodes promise to tackle storylines including racism, homophobia and fragile masculinity as characters respond to huge societal changes.
However, the new series also serves as a poignant farewell for main character Sidney Chambers (played by James Norton), and the introduction of a brand new series star.
As one crime-fighting vicar leaves, another one arrives, with actor Tom Brittney making his Grantchester debut as clergyman William Davenport.
Who is new Grantchester vicar William Davenport?
Not dissimilar to Sidney, William is a more modern man compared to the increasingly gruff Geordie (Robson Green).
The newcomer arrives on the scene early in the first episode with a natural swagger – and a leather jacket and motorbike.
Brittney tells RadioTimes.com that in the first episode, “You only get to see a bit of who he is.”
The 28-year-old actor adds, “What drives him is that he wants to be a good person and wants to help people by being a wonderful vicar that people love and trust.”
As always with Grantchester, however, there’s more to the newcomer that meets the eye. “There’s a dark past underneath that makes him that way,” Brittney says. “William has flaws and things he’s running away from.”
Viewers will have to wait and see to discover exactly what Davenport is running away from, with his traumatic past only becoming apparent in later episodes.
“There are places that we go to which are quite upsetting,” Brittney reveals. “A lot of stuff comes out about him and that was really hard to play. That was quite depressing, but fun to watch I think.”
These revelations are what tie Geordie and William together, with Geordie himself suffering with the departure of his closest friend.
While initially wary of one another, the bond the two form as the series progresses offers a different dynamic to what viewers have become used to with Geordie and Sidney.
“The idea that a detective and a vicar would work together is quite far-fetched anyway, but Grantchester makes it work perfectly,” Brittney says. “But the idea it can work again…that’s quite tough and they acknowledge that.
“To start with, Geordie and Will have a tetchy relationship. I don’t want to help him out and he probably doesn’t want me to help him out. It then becomes a different thing, like a father-son relationship, with mutual respect.”
Having announced his exit from the show last year, Norton has since promised his ending will be hugely poignant for fans.
“The final scene is very sad,” he explained. “It’s been a real joy to play Sidney. I’ve loved every minute of Grantchester and owe a lot to the show.”
While Norton’s co-star Robson Green teases that Sidney makes quite the explosive exit from Grantchester (“Two words: disused mineshaft,” he jokes to RadioTimes.com), Brittney reveals Norton’s departure was “lovely and heart-warming” – with room for him to return to the series should he so wish.
“I’m sure there could be [scope for his return],” he says.
However, Grantchester would need to be big enough for two crime-fighting vicars, with Brittney insisting he wants to stay in the series “for as long as it’s on for.”
This is Brittney’s biggest role to date, he explains: “It’s both scary but really satisfying as an actor because you always want to be out playing beefy roles.
“Those one episode roles are wonderful as well, and I love doing them. I’m proud of every single show I’ve done on my CV, but [Grantchester] was definitely a step up. And I’m lucky to have felt that it wasn’t as scary as it could have been.”
What else has new Grantchester star Tom Brittney been in?
Having starred in BBC1 lottery drama The Syndicate and Channel 4’s sci-fi caper Humans, one of Brittney’s more prominent roles includes the sinister Roger Lockwood in 2017 American drama series UnReal.
“Playing a chaplain is quite different to playing a rapist!” he says. “UnReal was fun but it was a really horrible part to play.
“You do worry about being typecast. If you play it good enough, and people think you’re that sleazy or creepy or whatever, then you kind of are worried. I like to play it well enough that people believe the character – but hopefully they didn’t think I was Roger because he’s a terrible, terrible man.
“It’s not something I enjoyed doing, though Grantchester I enjoyed every day.”
But it may be his role as fan-favourite Lieutenant Jeremy Foster in Outlander (above) which will prepare him most for the fame that Grantchester looks set to bring him.
“Outlander is similar to Grantchester due to its fanbase,” explains Brittney. “With both shows, they have incredibly devoted fans. Outlander fans still send me birthday cards!
“I was only meant to be in it for a few episodes, but because of the fans, they brought me back. To kill me.
“I have to thank Outlander for a lot of stuff, and thanks to the fans of the show.”
But does Brittney worry he may not be such a big hit with Grantchester viewers devoted to Norton’s Sidney Chambers?
“As long as I’m not getting hate mail, it’ll be fine,” he laughs. “I saw all the fans that he had on set, and people really love James Norton. They love the show, but they really love James Norton.
“Hopefully they’ll like me as much as they like James and the show.”
Grantchester series four begins on ITV on Friday 11th January at 9pm
Sign up to the Radio Times newsletter for the latest TV and entertainment news