Based on Sophie Hannah's novel series and also starring Olivia Williams, series two of Case Sensitive is based on the 2009 book 'The Other Half Lives' and sees DS Charlie Zailer (Williams) and DC Simon Waterhouse (Boyd) back to solve another twisted crime.
Digital Spy got Darren on the phone to chat about the new episodes, his recent success and whether he's planning to fit more Case Sensitive into his busy schedule...
Were you happy with the reaction to Case Sensitive last year? It averaged 6m viewers on its debut...
"Ecstatic - are you kidding, absolutely! For that reason, the fact so many people watched and apparently enjoyed [it]. And also personally because it was a drama and that felt good for me to be stretching those little muscles."
Sophie Hannah's novels have quite a rabid fan base - did you get a sense of the fan reaction to the first series at all?
"Yes. Firstly the support from Sophie herself was phenomenal. You work with a lot of writers and sometimes they differ in their willingness to hand over [their work]. Sophie was probably one of - if not the most - generous, selfless writers. She sort of put it in our hands and let us run with it.
"So to have that endorsement initially gave us huge confidence. Then the fan base were… obviously you're always careful of what you read, how many forums you visit, or how many Twitter pages you get invested in, but what I did see was fantastic, I felt that they got it.
"We'd honoured Sophie's material and the characters - we put them on their feet and fleshed them out, but we'd been very true to Sophie and I think that was respected."
When did you find out for sure that you were a hit and you were coming back for new episodes?
"I think it was quite soon after the first one went out - there was very good feedback from ITV. I think there was talk quite soon after. Once things are confirmed, they get kind of logged in pretty quick.
"So I'd say probably within a month of the other one going out, we knew we were probably going to go again. What's good is, because of the fan base that you've mentioned, you're working from such a library of source material that the thing's got legs before you've begun.
"You've got this pool of work to use. It's a short cut from deciding to do more and being able to do more. It's just a case of deciding which of the books to go to next - it's a luxury."
Is there a confidence that comes with knowing you're a hit?
"No, because I think you always go into the new project wanting to do the best version you can. You're not repeating the first one, so you don't have the guarantees of the first one; you have all the insecurities and the self-enforced pressures of a fresh project.
"We also have a new director and we have a new writer so there's a very different dynamic. So you want to have that fresh feeling, but have all the things that you felt were successful and the audience responded to [about the first series].
"So it's a brand new marriage and it brings with it a whole new anticipation. But that makes you work hard and pitch in and not be in any way complacent, because that would be foolish and wrong."
For those not familiar with the original novels, can you hint at what these two new episodes might be about?
"The licence we do take with the books is, if I can separate it into plot and relationships… Plot wise, when we've chosen the book, we very much stick to Sophie's brilliant plot and structure. You wouldn't want to deviate from that, because that delivers in genre terms everything that we would hope for and anticipate.
"Where we do take a bit of licence is with the Simon and Charlie characters, with the chronology of their relationship and the stage and development of it. The chronology is altered in that sense."
Last year, you mentioned that you used key passages from Sophie's books to help you understand the Simon character. Is that still the case or do you feel that you can just rely on the script now?
"I think Sophie's material is the bible, and you constantly refer to that. Sophie - in the first one and in this one - would bookmark sections that she thought were relevant. I'd read large chunks of most of the books, and I read some of the books all the way through, and chunks of the relevant passages.
"But Sarah Williams who wrote the script is fantastic, and in fact Olivia and I were very kindly invited into the early discussions. We had just a little bit of input which I was certainly very grateful for."
It's been a crazy couple of years for you - Case Sensitive, Holy Flying Circus, Spy, Dirk Gently - does it ever feel overwhelming?
"It feels busy, and I'd like more please! You work very hard to deliver and hope that work begets work. Sometimes there are gaps in between and sometimes things kind of stack up and you can get tired on the surface. But no, I wouldn't have it any other way. Last year was phenomenal for that reason.
"What's just as exciting is that I'm doing what I've been intending to do for a while, which is walk the line between comedy and drama. That's been important to me for a while. It's nice to be known for something and you get opportunities for that reason. But at the same time, you have to keep growing, and challenging perception, otherwise you plateau.
"I don't want to bore people or myself - to be busy is something to be grateful for, but to be busy doing diverse work is absolutely… I wouldn't change it for the world. I feel very lucky for that."
And are you hoping to fit a third series of Case Sensitive into your busy schedule?
"Absolutely, I think there's huge scope… we've got cases and storylines coming out of our ears, thanks to Sophie, we've got a wealth of material there. And with these two characters, particularly with this one, we've upped the dysfunction and we've really started to get a handle on who they are.
"I won't say the word 'relationship', because it's more a situation. I really think that's the thing that has had the universal element, that's the thing I think people will invest in and want to see more of, I think there is the scope for that.
"So with the combination of the two, if things go well and people like it as much as the first one - and I see no reason why they shouldn't - we could be doing this for a while and I would be very happy if we did that."
Case Sensitive returns on Thursday (July 12) at 9pm on ITV1.