David Caves on the return of Silent Witness: "They should have named the whole series 'Jack Gets Wet'"

Despite having a close shave with death himself, Jack is back as strong as ever this time around, but Caves concedes the events of the previous run are still taking their toll on the character, at least to begin with. "The ripples of that are still very much there," he says. "Jack and Nikki find themselves alone in this big building sort of knocking around a bit. There's, you know, there's obviously sadness and it's a little bit forlorn to start with. And with Clarissa's departure as well, obviously for Jack, he's a little bit sad he's lost his buddy there.

"But you know, quickly things... stuff happens, and they've got to get right back to work. So there's not a lot of moping around, shall we say."

The series certainly opens with a bang, with the first double-header focusing on a case that reopens old wounds for Nikki. Long term Silent Witness fans may recall a memorable episode back in 2010 that focused on a university shooting, and this time around when Nikki is called into a high-security prison she immediately spots someone she's certain was the perpetrator from that historic case (Elliott Tittensor reprises his role). Naturally, her partiality is somewhat affected in the proceeding investigation, and it falls to Jack to keep her in check.

"It's always good if there's something very personal at stake within a case," Caves explains. "And then obviously it compromises our impartiality, which is dramatic and fun to watch because the character finds themselves in this very tricky position. So that's where she finds herself – Jack is trying to steady her and trying to get her back on track and try and be a little bit more about the evidence, not so much about how she feels it should be. And that's the kind of tug of war we always have with it, which I think is great. Both the characters like to kind of balance each other out. And that's kind of a big part of our relationship."

The synopsis for the series teases that Jack and Nikki will be pushed increasingly close together over the course of the 10 episodes, and Caves says that in some ways the relationship between them reminds him of his early days on the show back when he first joined in 2013 – when he says they were something of "a dynamic duo".

"It's great because we sort of get to go back there and rediscover what that is and what our relationship is not," he explains. "We've gone through an awful lot together, and so there's a lot of stuff there, there's a lot of material to draw on, feelings to draw on, emotions to draw on. So it's not just a simple case of two colleagues, there's deeper stuff going on, in there... just little glimpses of stuff which hopefully the audience will like and be intrigued by and wants to know more about."

Of course, there's also the small matter of a new cast member – with Jason Wong set to join the series as pathologist Adam Yuen from episode three onwards. And while Caves says that Wong was "lovely" to work with, the working relationship between Jack and Adam is initially not quite so healthy. Upon Adam's arrival at the Lyell, Jack rather takes against what he perceives to be a somewhat cocky attitude, and there is a certain amount of friction when they work together on their first case. Caves puts that down to Jack being a "naturally suspicious person anyway" and also reckons the recent departure of Clarissa might have made him even less welcoming to a newcomer than usual.

"He's a bit cocky, he's a bit full of himself, and he's sort of stepping on my toes a little bit," he explains. "Kind of what Clarissa would have done originally, he's sort of taking up that mantle a little bit. And so of course, it's going to rub him up the wrong way. And especially because his demeanour is, as I said, a little bit full of himself a little bit ahead of himself, too confident. And so yeah, it causes some sparks initially. But I hope they're amusing as opposed to being heavy or angsty kind of like 'I hate you'. It's not that, it's just kind of amusing workplace banter."

As for Jack's family life, fans can expect all sorts of developments this time round – with Richard Durden once again starring as his father Connor, a surprise reappearance for Owen McDonnell as his jailed brother Kevin and even the emergence of a mysterious new family member that he'd previously had no idea about. It's certainly a complex – and somewhat dramatic family life – and Caves jokes that it might make for a good reality series.

"We always have a laugh about Keeping up with the Hodgsons," he says. "I think there's a gap in the market for it. There's no more Kardashians, and so I think it's time for the Hodgsons. I've pitched it and they're gonna get back to me...

"But yes, there's so much going on family-wise for Jack," he adds. "It's like a real headache for him in a good way. Because he's trying to balance his very complicated family life with his very complicated work life. And there's not a lot of time in between, for him to just relax and just have a moment. So it's great for the character because he's been dragged from pillar to post."

There's lots more to come as well: Caves is hard pressed to pick out a favourite storyline from the new batch of episodes, but he is keen to point out the exciting list of guest stars assembled for the new series, which includes Kevin Eldon, Ann Mitchell and Lorraine Ashbourne. And Jack also finds himself thrown into a couple of interesting situations that allowed Caves to explore another side of the character.

"There's a really good episode that's set in sort of the underground boxing world," he says. "So that's a really cool one. Because obviously, my character is a bit of an MMA guy who's very into boxing, and all that sort of stuff as well. So it's great for the character to get taken into that world again, we don't see him, we don't see him doing any actual official fighting, but he might get into a little scrap here and there, which was good craic.

"I think the mentality of a fighter is something I'm very interested in anyway," he adds. "I'm not one by any means at all. But I love it, I'm very interested in it and think it's fascinating. And so to have a character who's on one hand, very scientific, very evidence-based, very practical, and then on one hand, he's a bit of a hothead, he's not shy sometimes about using his fists. I don't know, I think it's a really interesting thing to get duality for a character because he's unpredictable. I think that's dangerous. And that's kind of cool. So I always try and try and remind them to drop something in where appropriate."

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Less fun for the actor was Jack's frequent battles with water this season, with Caves joking that they should have named the whole series 'Jack Gets Wet' – and light-heartedly lamenting the freezing situations he frequently found himself in during production. "They've got me running into the ocean in the English Channel in December," he says, "They've got me wading into rivers. They've got me waist-high in floodwater. They had to build this tank of water that was supposed to be the interior of a room, because they couldn't flood the actual room so they had to build this separate thing and filled it with icy cold, I mean, it was colder than the sea this water! Could they not have heated it a little bit?"

Perhaps the most fun time Caves had on set was in the very final double-header of the series, which boasts an excellent cast including the likes of Sian Phillips, Pauline McGlynn and Nicholas Woodeson. The episodes see the Lyell crew holed up inside a care home after a massive storm cuts off all the electricity, and they soon form a close bond with many of the residents – while also trying to get to the bottom of a mystery. Caves says the whole storyline plays out a little like a "real-life version of Cluedo" and describes it as "possibly the funniest thing I've ever been involved with."

"It's kind of quite an ornate drawing room in this care home," he says. "Our clothes have all been soaked, we have to change into sort of old people's clothes – so we're sat round in this kind of slippers and jumpers that are too big for us and stuff. The electricity's gone and we've all got torches and we're finding bodies here and there, and Nick Woodeson plays this wonderful old character who used to be an actor, so he's constantly quoting from King Lear."

It's clear from listening to Caves talk about the show that almost nine years after first taking on the role he's still just as passionate about Silent Witness as ever, and with a 25th series having already been commissioned he says he has no intention of leaving any time soon.

"I love it, it's a great job," he says, "I love working with those people. I know it always gets very saccharine and sweet around this time, it sounds like a big love-in – but it sort of is, and we're all friends and we do actually genuinely like hanging out and coming back and working together.

"I was just in there the other day in the studios, for the first time again, just for a quick hello and a quick meeting and stuff, and it is a joy to see everybody, find out what everybody's been doing and how everybody's been keeping and getting through these tough times. So to be working at a time like this and to be working on a really good show, a show that I really enjoy doing – it's just a privilege. So long may that continue."

Silent Witness returns to BBC One on Monday 6th September at 9pm. Check out what else is on with our TV Guide, or visit our Drama hub for all the latest news and features.