Torchwood star John Barrowman and his sister Carole talk about their collaboration on their first children's novel, Hollow Earth, a tale of 12-year-old twins with supernatural powers. They insist they're not trying to take the place of Harry Potter - even though a movie and TV deal is almost in the bag.
By Hannah Stephenson.
John Barrowman welcomes me into his Chelsea home dressed in his pyjamas, hair tousled, unshaven, but still looking strikingly handsome and clean-cut.
He shows me up the spiral staircase to the first floor of his elegant house, which opens up to a large open-plan area adorned with plush leather sofas and quirky Union Jack cushions.
His sister Carole, who is eight years his senior, may not be as physically striking as the man himself, but she shares the star of Torchwood's sense of mischief and fun.
They are both warm, funny - and very loud. Although we're sitting close together at his stylish glass dining table, he speaks as though he's projecting himself to a large audience in a theatre.
Together they make an intoxicating, effervescent duo, constantly interrupting each other, one starting a story, the other finishing it off, and there is constant laughter.
It's clear this is a close family. John, 44, who has made a mint from a career that started out in musical theatre and then expanded to TV, flies his parents over from America (where he grew up) regularly and has bought life-changing luxuries for the wider family over the years, including cars and houses, and put his nieces and nephews through college.
When considering this, Carole looks at him with puppy-dog eyes, suggesting jokingly that it might be about time he splashed out on her.
She's a journalist and professor of English in Wisconsin, who previously collaborated with John on his two autobiographies, Anything Goes and I Am What I Am. Now, they have written their first children's book, Hollow Earth, aimed at nine to 12-year-olds.
It's an exciting page-turner about 12-year-old twins Matt and Emily Calder, who can not only read each others' minds but have supernatural powers of imagination that enable them to make art come to life and enter paintings at will.
"My thoughts are much deeper than his," says Carole dryly, on the subject of brain power.
"But I can make money out of my thoughts," he counters.
"We didn't hang out with each other as kids because of the age difference. But since we started working on books together, sometimes I'm over three times a year," she explains.
"And she's here for a month at a time," he laments.
It's amazing that Barrowman has managed to fit projects involving his family into his busy work schedule. He's starred in a succession of West End musicals, been a talent show judge with Andrew Lloyd Webber, skated in Dancing On Ice and hosted his own Saturday night show, Tonight's The Night, on BBC One. He's devoted to his long-term partner Scott Gill, an architect who's been with him for 19 years (they became civil partners in 2006), and to his wider family.
When he and his sister are working together, they tape their conversations in case an idea is formed, with John tending to be the creative force while she does the writing, he explains.
In the novel, the twins' powers are sought by villains trying to access the terrors of Hollow Earth, a place where all the evil creatures ever imagined lie trapped for eternity.
It's awash with devils and demons, set against an atmospheric backdrop of an ancient abbey on a remote Scottish island, where much of the action takes place.
But the Barrowmans were keen not to emulate a scene from a certain school of magic.
"I don't want people to think that we're writing the next Harry Potter because we're not," John asserts. "We just wanted to write a really good story."
Yet he admits they wrote it with a TV series or film in mind and are currently negotiating rights in a deal that would see John's production company make the series, in which he would star.
They've also been approached by a Hollywood film company, so there may be a movie deal too.
However, they were inspired by the effect the Harry Potter books had on Carole's two children when they were younger, John explains.
"I used to buy the first editions and ship them over to my niece and nephew so they had them before all their friends. We were at a cabin in Wisconsin, by a lake where there's plenty for kids to do outdoors, and we looked through the window and all the kids were just reading these books," he recalls.
The supernatural elements of Hollow Earth stem from their love of science fiction, as they grew up in the era of Doctor Who and Star Wars.
"I love the fantasy element and going into these different worlds," John enthuses.
While Carole and John are not twins, the relationship between them isn't dissimilar to their main characters, they agree.
"There's a bit of both of us in Matt and Em," says Carole. "We worked hard on the book to have the dynamics of siblings. He annoys her sometimes and she annoys him, yet if they were in trouble they'd back each other up."
"He was really an obnoxious child," Carole continues, eyeing John accusingly, him nodding in agreement. "I was eight when he was born so I was old enough to recognise just how obnoxious he was. One time we locked him in a closet."
"That's the story of my life," John observes wryly.
Born in Scotland, before the family decamped to Aurora, Illinois in 1976, the pair both speak with a Scottish accent at times, which then drifts into an American lilt. John has homes in Wales, London and Los Angeles, and is constantly on the move with work.
The family - John is the youngest of three children - moved when his dad was put in charge of the Caterpillar tractor manufacturing plant there.
In Scotland, he received a no-nonsense upbringing, while America gave him the get-up-and-go attitude that has led to his hugely successful showbiz career.
He's just finished filming a documentary on the remake of Dallas and a pilot TV show, and has been approached to appear in two American TV series.
While Carole is in England promoting Hollow Earth, they have also begun working on a Torchwood novel, as well as the second book in the children's series. So, could it end up being another Harry Potter phenomenon?
John says: "If people compare us to Harry Potter, it would be awesome. I love reading those books and watching the movies. It's ironic that's all coming to an end, but we're chuffed that people are already saying, it could be the next Harry Potter."
:: Hollow Earth by John and Carole E Barrowman is published by Buster Books, priced £6.99. Available now