Stay Close stars talk Ken and Barbie – the 'musical theatre murderers'

Indeed, the mysterious couple are quickly revealed to be ruthless killers, but the motivation behind their crimes is not made clear until later in the eight-part miniseries.

So, what on earth could have inspired these bizarre characters? Novelist Harlan Coben explained that his inspiration for Ken and Barbie originates with a standout memory from his younger years.

"At half-time in NFL football games in the '70s and '80s there used to be group called Up With People, who would perform this really wholesome act," he recalled in a statement to the press.

"They would sing all these Kumbaya-type songs and they had these fake painted smiles on. I’m sitting there going, ‘There’s got to be more behind those fake painted smiles.’ So I decided, wouldn’t it be cool if two of them were kind of psychotic killers?

Coben added: "They are the moments in the show where you go, ‘What the-- where are they going with this?’ I kind of like that. I think Ken and Barbie keep us off balance a little bit. And yet as outrageous as Ken and Barbie are there is something about them that feels grounded and realistic."

Stay Close star Bethany Antonia described the duo as "bonkers in the best way", telling RadioTimes.com about a scene she shares with them later in the series, which unfolds in a secluded log cabin in the forest.

"It was as surreal as it probably looks, because every time we would do a take we would do the whole scene. So I was in the cabin even when there were no cameras in there, just so that Hyoie and Poppy could have something to play off of.

"So, being in there and reacting to it off camera was the exact same as seeing it on camera, because they are just terrifying... I really am intrigued to see what people make of them."

As for the dance routines they perform throughout the series? "They didn't have that much rehearsal either. They just pulled it out the bag so much... they look phenomenal," she adds.

In an interview with RadioTimes.com, Stay Close star Richard Armitage also weighed in on the delightful oddity of Ken and Barbie, revealing that they presented quite a "challenge" for the creative team to overcome.

"They’re a couple of characters that you really enjoy in the book and actually weaving that into a screenplay and making it believable was probably a more difficult task than anything else," he said. "Because to have a couple of musical theatre murderers, I think was a real challenge. But obviously, brilliantly cast."

Indeed, Stay Close director Lindy Heymann was thrilled with the end result, even suggesting that we might not have seen the last of Ken and Barbie's disturbing partnership.

"I would be very surprised if at some point someone doesn’t suggest that there could be a Ken and Barbie spin-off show," she said. "Their early years and where they met is all described in the book. They are brilliant characters played by Poppy Gilbert and Hyoie O’Grady... The chemistry between those two was amazing."

For more on Ken and Barbie, check out our guide to the Stay Close cast.

Stay Close is available to stream on Netflix. Read our guide to the best series on Netflix, check out more of our Drama coverage or visit our TV Guide to see what's on tonight.