Endeavour is "darker" in series six – and that suits Shaun Evans just fine

Really, I don’t want him to downplay anything. I’m just trying to keep up with a 38-year-old who pulses with the enthusiasm of a man half his age. In our hour together he tells me about his decision to direct as well as star in Endeavour, why he drives himself relentlessly to learn more about the world, the reason he doesn’t go boozing any more, and just how much he cares for the people he works with. “l really love these guys,” he says of the Endeavour team.

He also asks me not to write anything that suggests he has anything but the utmost respect for his colleagues. “I’m always wary,” he says, “I’m just going to say that now.”

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He’s wearing slimming dark navy trousers and a shirt, but there’s not an inch of fat on him. He looks like he does on television, focused and very serious.

Evans has played Endeavour Morse, the younger version of the detective made famous by John Thaw, alongside Roger Allam’s DCI Fred Thursday, for seven years. With writer Russell Lewis and executive producer Damien Timmer, Evans is one of the key people who steers the hit show’s direction. “And Rog,” Evans adds.

Such is the chemistry between Evans and Allam, I suggest it’s their relationship, rather than the will-they-won’t-they tension between Endeavour and Thursday’s daughter Joan, that is the real romance at the heart of the show. “Yes,” says Evans, mulling this over as he mulls everything. “I’d agree.”

They first appeared together in a 2012 pilot. Five full series followed, and now Endeavour is back for six feature-length episodes, the second of which Evans has directed. Having directed episodes of the long-running medical drama Casualty before, Evans says he’s determined not be limited to acting. “Even if Endeavour was to end now I feel I’d be able to go and direct something and it wouldn’t be second best.”

The last series of Endeavour finished in disarray, when Lewis Peek’s rookie constable George Fancy was gunned down and WPC Shirley Trewlove, played by Dakota Blue Richards, left for Scotland Yard. Now the 1970s are in sight and hard drugs have hit Oxford.

DCI Thursday, after postponing his retirement, is working under a thoroughly unpleasant and possibly corrupt new boss, and a rueful Morse is manning a rural station, back in uniform and sporting a large moustache. “When Fancy got killed, I thought Morse felt responsible for that,” Evans says, explaining the moustache. “So, there was an idea of asking, ‘What about not being able to look in the mirror? What would take you away from yourself?’”

As ever with Endeavour it’s the atmosphere that matters. The souring of the 1960s is signalled by brutalist interiors and lots of Led Zeppelin, and the show also seems more willing to show the bullet holes and wounds than before. “Well, it’s always a compromise,” Evans says. “ITV have specific guidelines about what they want and don’t want to see at a certain time. But I think as a storyteller, you’re interested more in the darker aspect of things. Often, it’s where a lot of the gold is.”

The series, as complex as ever, is less concerned with tying everything up at the end; explaining what has happened has never really been what Endeavour is about. “That’s very astute,” says Evans, as if he’s finally found someone who agrees with him. “I find it dissatisfying when I watch something and then walk away and I’m still thinking afterwards, ‘He bought those stamps and sent that letter, but how could he have done that?’ That annoys me. So I always seek clarification on that. Sometimes you get it, sometimes you don’t.”

Evans was born in Liverpool in 1980; his father was a taxi driver and his mother was a health worker. “My family originate from Ireland and that was a massive part of my culture growing up,” he says. “I feel as close an affinity with that as I do with being from Up North. One of the great things about being an actor is you can leave all of that behind – just crack on and do your work. Now I’ve lived in London as long as I lived there.” Does he worry about becoming a Londoner? “Yes, or of losing a big part of who you are. It’s funny, isn’t it? You spend so long pretending to be other people, then as soon as you go home you’re right back into it.”

When Endeavour began, Evans based his portrayal of young Morse’s voice on that of Michael Palin, another young northerner who found himself in Oxford in the 1960s. He still does. “I was listening to one of his CDs the other day. I get a new one for the series.”

I’m surprised to hear how much of Merseyside remains in Evans’s own voice. “For good or ill for someone in my game,” says Evans. “I was reluctant to do much press for this way back because I thought, ‘Well, as soon as people hear what you sound like, it’s game over, isn’t it?’ I like having a bit of separation.”

When he was 11 years old, Evans won a place at St Edward’s College, the highly academic Liverpool school run by the Christian Brothers. “I was raised as an Irish Catholic,” he says. “It’s always there, but I don’t really have any religion. I have a system of my own personal beliefs, which are informed by many different things. I’m kind of interested in studying the gospels, but just as interested in the origins of Europe.”

For half the year Evans is filming Endeavour; the other half is dedicated to a sort of restless search for knowledge that can take him around the world. “I can afford to take six months off,” he says. “I love my work. But if I’m not doing that, I’m taking pictures, I’m writing every day, reading books. The first job I ever had was in a camera shop, so taking pictures and being interested in photography and developing has always been a part of my life. Writing as well. I want to be better. I want to improve as best I can.”

Can he reveal any books, television series or films that may emerge from this creativity? “No, not right now,” he says. “You would look like a prat if you said something and then it didn’t happen.”

Does he ever just take a break? “Of course. You do things that you like to do, but I also like to generate my own work as well, otherwise I’d just be sitting around. You need other things going on. In a way it makes no odds, regardless of how much you’re getting paid. That’s a by-product, isn’t it?”

That rather depends, I suggest, on how much you’re being paid. “I hear what you’re saying,” he concedes. “If you’ve got to run out and get another job. But I think it can be equally dangerous having that luxury, and damaging to someone in my line of work.

“For those six months there’s so many things that I’ve thought about that are interesting, and I want to make sure that I make the most of them. I’m also going to be working with different people, seeing different parts of the world and seeing how different people do different things – photographers and film-makers. And also studying the history of things as well. There’s so much to do…”

He doesn’t tell me if he has a partner, but I imagine Evans would be hard to go on holiday with. “Yes, a nightmare,” he says, “If I went and sat on a beach I’d last about two days.”

I wonder if he ever does anything that isn’t serious or intelligent? “Like what?” Deciding to drink yourself silly this weekend, perhaps. “I’ve done that,” he says. “It’s not like it doesn’t suit me. I just feel like time is of the essence, and I want to work. There have been times when I wasn’t as productive, but I don’t think I was as happy. I’ve realised what keeps me happy and what keeps me going. Seeing things, mates who inspire me to be creative. Not being hungover for four days, and losing those days? Drinking is amazing. I love all that but, right now, I’m into doing my work.”

And finally, I ask, will the series ever come full circle and end in 1987, when the original Morse began? “No,” he says with certainty. “We won’t do that.” Will there at least be another series? “If we reached the destination of the story in this series,” he says. “If we felt that we’d seen it all, then we all have to be brave and say, we’ve done that now.”

He ends as intensely as he began. Feeling a little blown away, I take the wrong corridor when we part and go down a dead end. I turn back, round a corner and find Evans again. He’s hugging Roger Allam by the lifts.

Endeavour airs Sundays at 8pm on ITV