The mystery isn't why one of American TV's most successful British stars is in Swansea - the mystery is from the pen of the celebrated crime writer Agatha Christie.
Hugh Laurie and fellow actor Will Poulter have both been spotted in the city over the past week, prompting speculation as to why they are in town.
And they've now been spotted doing their day job, out filming on location on Gower.
According to Hollywood entertainment website Deadline, the pair are working on a Britbox adaptation of 1934 Agatha Christie novel, Why Didn't They Ask Evans?
The website says Hugh Laurie is working as director and executive producer on the production, one of the streaming service's biggest commission to date.
READ MORE: Hugh Laurie and fellow acting star Will Poulter walk into Swansea Marina restaurant
The story, first published in 1934, tells the story of of Bobby Jones and socialite friend Lady Frances Derwent who discover the body of a man while playing golf, and who take it upon themselves to find the killer.
In addition to The Revenant star Poulter, who plays the title of role of Bobby Jones, and Bohemian Rhapsody's Lucy Boynton as Lady Frances Derwent.
It also features Game of Thrones star Conleth Hill as Dr Alwyn Thomas, Miles Jupp, from The Durrells, Paul Whitehouse and Morwenna Banks.
Deadline says Laurie signed up to write, direct and executive produce the production in April.
He said: “The hairs on the back of my neck haven’t properly settled down from the first time I grasped the beauty of the essential mystery.
"Since then, I have fallen deeper and deeper in love with the characters, and feel immensely honoured to have been given the chance to retell their story in this form.
“I will wear a tie on set, and give it everything I have.”
The 62-year-old star has now been spotted with his cast at Three Cliffs Bay.
It is being made by filmmakers Mammoth Screen, which has previously made films of Christie books And Then There Were None and The ABC Murders, starring John Malkovich.
Mammoth’s director of television and executive producer Helen Ziegler said: “Hugh's dazzling scripts take the mischief and cleverness of the original novel to a new level, and with Hugh sitting in the director’s chair, this really is going to be an authored treat for Christie fans everywhere.”
“I’m deeply honoured to have been given the opportunity to co-lead this project with Lucy and the chance to bring Agatha Christie’s thrilling story to life under Hugh’s direction,” said Poulter.
“I’m so thrilled to be working with Hugh and Will, and on this story from one of my favourite authors. I can’t wait to get started,” added Boynton.
