Vigil is returning to BBC One in December, two years after the premiere of season one, which saw Suranne Jones' detective Amy Silva tasked with investigating a mysterious death on board a Royal Navy submarine.
The upcoming season will see Amy and her partner in life and work, Kirsten Longacre [Rose Leslie], look into multiple unexplained fatalities while entering into the world of drone warfare. Life is a little more complicated for the couple, however, as Kirsten is expecting their first child when Amy is assigned to the case.
During a Q&A event, Suranne and Rose spoke about the development of Amy and Kirsten's relationship in season two, with Rose teasing that the pair are "torn apart" yet again.
When asked what brought them back to the series for another instalment, Suranne explained: "The characters, the fact that our relationship is in the middle of such a big thriller. The heart of it is the two of us and I was really interested to see where we went, and the fact that one of us was having a baby kind of helped.
"It sits so well in this huge show. The scope of the show is so big compared to the last one, and we managed to sit at the heart of it. I wanted to go back and explore it."
Rose added: "I liked the idea that being pregnant meant that Kirsten had to stay home and be in Scotland, and as a result, that tore us apart again in a very natural, organic way. I felt that certainly coming from that premise, it helped that there was a reason as to why their relationship was going to be torn again."
Speaking about the growth of Amy and Rose's relationship in the upcoming episodes, Suranne revealed how the couple "butt heads" as they juggle work with their expanding family. "What I found about the development of our relationship is these are two women that have decided to have a family together, they already have a daughter, a child on the way, but they're also very defined by their work, by their careers," said the Doctor Foster star.
"So they're gonna start butting heads, when one is trying to look after the other, and the other wants to do everything. And I think it brought an element of fun, but actually a seriousness of 'Well how does that change the relationship dynamic?', which was really interesting for us. And it took it somewhere else."
Series two sees the couple drawn into the world of drone warfare following multiple deaths at a Scottish military facility.
The six-parter will premiere on Sunday 10 December, with the first three episodes arriving on BBC iPlayer at the same time. The show will also air over the course of just over a week, concluding on Tuesday 19 December.