Tense investigation and police corruption pair in the sixth—and reportedly final—season of Line of Duty

Should you be intimidated by the thought of entering the world of Line of Duty five seasons in, take Kelly Macdonald’s word for the fact that it’s never too late to make the leap. “I hadn’t watched the show,” admits the Scottish actress, who joins the series in a sixth season that’s also rumoured to be its last. “I knew about it, and I was very interested when I got the offer, because I knew that it would be a good challenge. They’re great parts—you get to play the lead in an amazingly well-written, successful TV show for one season—so I wanted to do it.”

Line of DutyBritBoxThe Boardwalk Empire alum portrays DCI Jo Davidson, the show’s latest “guest lead.” She’s the officer tasked with solving the murder of a journalist who’d been digging into police corruption. Somewhat ironically, her unconventional techniques make her a target for our heroes at Anti-Corruption Unit 12 (AC-12).

To prep for the role, Macdonald dug into previous instalments and found that “it’s just completely compelling television. It’s a lot of police talk, and it sort of doesn’t matter how much of it you understand or if you know what all the acronyms stand for, you just go with it. And it’s exciting! It’s funny, you hear people being against watching anything with subtitles, but for some reason, this police talk really appeals to people, even though it’s the same thing as another language.”

Line of DutyBritBoxAs with the police jargon, Macdonald’s character is a bit of a conundrum. DCI Davidson comes off as a straight shooter, but soon starts to make decisions that are questionable to those around her. But is she a police officer with no patience for protocol or yet another dirty copper in league with the bad guys? “She’s entirely enigmatic and you can believe both things about her,” says Macdonald. “You’re kind of one way or the other with her, and that was interesting to play with.”

In doing interviews for her season, the actress kept being asked if her character is “H,” the last unidentified member in a cabal of bent cops that AC-12 has been trying to unmask since the beginning of the series. “H was a funny one, because I didn’t know anything about the letter and what it meant. And before I started, I kept getting asked if I was H, and I was like, ‘I don’t know what you’re talking about.’ I hadn’t read enough of the scripts to know anything about it,” says the actress, who since then has learned the art of a good plot tease: “H is someone that needs to be discovered.”

To be fair, Macdonald only received broad strokes for her seven-episode arc from creator Jed Mercurio, which added to the challenge of playing the stone-faced Davidson. “You don’t know her story until you know her story,” Macdonald explains. “For a long time it’s, ‘I’m a detective’ and that’s as much as she’s giving away. Her life is entirely work. You get the feeling that there’s more going on—which there is—but I had to just be unemotional.” She also had to tackle that jargon, which Macdonald suspects goes as much over the viewer’s head as it went over hers. “I don’t know how many people take it on-board, because it’s really a lot of information. Even when you’ve got it written down in front of you, it’s quite hard to navigate. It is a bit different [expressing yourself through disseminating information] instead of having an emotional conversation with someone.”

Line of DutyBritBoxThe experience, in retrospect, felt like a unique one to the woman who first rose to fame with 1996’s Trainspotting, and has since worked steadily in both film and TV. “My career is good, but I make films that not many people see, and that suits me fine because I get to do the job that I want to do,” Macdonald muses. “I’m aware of how many people watch the show. And I’m aware that even with my mask on, people have started talking.”

In addition to being recognized more frequently, the series—which in past seasons has been guest-led by Lennie James, Keeley Hawes and Thandie Newton—is a great showcase for any actor. “When I was starting, Adrian Dunbar [who plays AC-12 Superintendent Ted Hastings] said, ‘It’s just a great way for someone to come in and show what they’ve got.’ And then that fills you with fear because you think, ‘Oh God, what have I got? I don’t know if I’ve got what it takes,’ ” laughs Macdonald. “But for this one, I couldn’t have been happier with the things I got to do.” And that wasn’t all murder and mayhem. “We had quite a lot of fun, considering we were filming during a pandemic. I find the scenes when you’re in a car quite fun to film, because you’re generally in charge of the radio. In between takes, you can play music and have a wee sing-song.”

Line of Duty streams Tuesdays on BritBox