Some important news if you’re planning to bump somebody off. Get in quick: Detective Inspector Humphrey Goodman – probably the world’s most successful murder cop – is heading back to the UK.

Yes, Humphrey, the endearing detective in Death in Paradise, is packing his linen jacket and heading home. Why? Because, after four series, Kris Marshall has decided it’s simply no longer practical to spend six months of the year 4,000 miles away in Guadeloupe, the paradise island that doubles as Saint Marie.

When your home is in Somerset, your work is in the Caribbean and your eldest child has reached school age, something has to give. The star’s son, Thomas, was a baby when Marshall joined the hit series. But now that the little boy is starting school – and he has a baby sister, Elsie – Marshall has decided he can’t carry on ferrying his whole family out to the Caribbean.

The 43-year-old star says, “Every year except last year we took Thomas out with us. The only reason they didn’t come out last year was because my daughter was born and she was only three months old when filming started. Thomas has basically spent half his life in the Caribbean. Every year he went to the same nursery in Guadeloupe. But now it’s time for him to put on scholastic shackles and toe the line.”

Which explains why a new investigator is taking over Humphrey’s beat: DI Jack Mooney, played by Father Ted star Ardal O’Hanlon. The decision to leave did not come out of the blue, says Marshall. Producers have known his plans for some time.

“It’s something my wife and I discussed three or four years ago. When I was first offered the job, my son was six months old and my wife wasn’t working, so it was a very easy decision. We decided I would do Death in Paradise for a few years until it became impractical. It was always quite a finite thing. I certainly didn’t hide it from anyone I work with.”

New broom: new Death in Paradise star Ardal O’Hanlon as DI Jack Mooney

Indeed, Marshall gave a big hint when he first joined the show, telling RT in 2014: “If you’ve got children who are school age, it must be incredibly tough being away.” 

This is not, of course, the first time a new man has taken the helm at Saint Marie’s police station. When the series began in 2011, Ben Miller was in the lead role as DI Richard Poole. Miller passed the baton to Marshall after two series – he, too, was struggling with the strain on a young family.

Throughout its life, the show has grown and grown. Series one attracted an average of 5.8 million viewers. Pretty good, but compare that with the current figure: the first episode of this series brought in 9.2 million, when you include the people who watched it on iPlayer.

Marshall says there’s no secret to its success. When I last spoke to him, he described it as “a cross between Columbo and Scooby-Doo”. Sure, the sunshine is a boost in the middle of a cold, drab British winter. But the main thing is that the drama isn’t pretending to be anything it’s not. “We don’t take ourselves too seriously. People like to smile and they like a caper. And that’s what we are: a crime caper.”

Family matters aside, Marshall’s friends must think he’s crazy to give up a job that involves spending six months of the year on some of the world’s prettiest beaches? “Yes, some people think I’m mad, obviously. And there is an old adage, ‘Don’t quit a hit’, which is very true. I’m going to miss it terribly. There have already been times when I’ve thought to myself, ‘Have I made the right decision?’”

How have the scriptwriters dealt with Humphrey’s departure? Marshall doesn’t want to spoil anything, but viewers already know that a murder inquiry has taken Humphrey to London – where he finds himself working alongside O’Hanlon’s character. We also know how painful it was when Humphrey’s girlfriend Martha returned to the UK. Is it romance that makes Humphrey stay in London? 

Marshall is coy. “There are myriad reasons. Of which that may be one.”

I ask Marshall what advice he has given his successor. His answer revolves around the heat. When they’re filming outside, it can be up to 40° Celsius. And the indoor scenes are often even more unbearably hot – especially as Humphrey always wears a jacket for work (unlike the real police of Guadeloupe, who are all in short sleeves).

“I gave Ardal the same advice that Ben [Miller] gave to me, actually. When you’re filming the big wrapping-up scene at the end, make sure you know your lines backwards. Because we film it all in one day and otherwise the heat starts to get to you. 

“Secondly, always do your shots first in the morning, before the heat gets too much. Then, after lunch, they turn the cameras on to the guest actors and you can watch them fry!”

Will O’Hanlon’s detective, DI Jack Mooney, be very different from Humphrey? “Well, he’s Irish, for starters. So that makes a bit of a difference. His character’s a lot more anecdotal, so the way he goes about things is different. He’s also been recently widowed – and he has a daughter in her early 20s. So that’s a whole different dynamic.” 

Marshall adds, “I wasn’t there when he got his proper cop feet under the table, but I am hearing worrying talk from Guadeloupe that he was not wearing a jacket. Which upsets me greatly – we can all do it without a jacket. That way, it’s just easy. Then it really is just a holiday.”

This interview was originally published in the 11-17 February 2017 issue of Radio Times magazine