“Blue Lights,” which tracks three probationary police officers and their mentors in Belfast, has been a bright light for BritBox since its launch, three seasons ago.

In Season 3, now streaming, Constable Grace Ellis (Siân Brooke) makes a dramatically deep dive into her previously hidden personal history as the series takes a realistic look at the complications of living and loving fellow officer Sergeant Stevie Neill (Martin McCann).

“It’s been lovely to explore that dynamic between these two characters who’ve lived a life. This isn’t their first time around the block,” Brooke, 45, noted in a phone interview.

“They’re both older. Both, in terms of love and people, have been burnt in their past. So they danced around each other for the first two series.

“Then, it came to a point, ‘We can’t really do that anymore.’ They needed to dive into this relationship. But then you throw in the curve ball: Stevie’s promoted and has to be the boss.

“While Grace, she’s a character that doesn’t play by the rules. That puts another level into their relationship.

“They are a fully-fledged couple” Brooke added. “But they get blown apart by the revelations that are uncovered. Then we watch to see how they navigate that.”

Because the series has been following these characters in real time, with each season another new year in their jobs, there’s a question: Is Grace, who was formerly a social worker, getting burnt out?  Would she maybe look for something else?

“We realized through the research,” Brooke explained, “there is a thing called ‘The 2-year Fade’ within the force that happens.

“They’ve now passed probation and graduated. They’re proper police officers, proper cops, and at this point they are, I think all of them, slightly jaded.

“Possibly dissatisfied — with what they can achieve realistically within the job. Especially Grace. Because she’s a people person and she wants to make that difference, a direct difference with the individuals that she comes into contact with.

“I think she feels slightly ground down that her hands are tied sometimes. Because of the bureaucracy or the procedural stuff, the hoops that she has to jump through in order to make a change.

“This time around she is frustrated. But she’s not a rookie anymore. She has the confidence in her own ability to be able to trust herself.

“And people will see what happens within this season, whether it pays off or not. Right?”

“Blue Lights” streams on BritBox