Actor Hugh Laurie has left the sanitized American hospital of his TV series “House MD” and burrowed deep into shadowy British mystery. He has not only adapted one of Agatha Christie’s classic murder stories, but is directing “Why Didn’t They Ask Evans?” that arrived on BritBox Tuesday.

He says he was talking with the Christie estate about playing a role in another of her works when something weird happened. “I probably shouldn’t say which one it is because ... they've probably gone to Colin Firth now, let’s be honest,” he says.

“But in the course of that conversation, I just happened to mention ‘Why Didn’t They Ask Evans?’ I think I was just referencing some line or some moment, and they responded and said, ‘Oh, we are hoping to make that one day.’

“And I said, 'Well, there’s no role for me in it so I would love to be involved, but I wouldn’t be as an actor because I don’t see a role, but I’d love to try and write it.'"

They agreed, and soon Laurie was determined to both write and direct the piece because he finds this particular Christie puzzler unique.

“The real mystery is not who the killer is,” he says. “I mean that is a mystery and we have to track that down and he or she must be apprehended and brought before the law. But the REAL mystery is what does the question of the title mean? It’s like a 100-dimension Wordle where you’re trying to solve this puzzle, and until you solve it, it’s not really satisfying,” he says.

“You might catch the killer, but until you understand, decipher the question and answer the question, it doesn’t really satisfy. And I think that is her genius. Agatha Christie, who was the most astounding mystery plotter of all time — I mean, I can’t think of anyone else who really comes close — I think she knew that. I think ... she said, ‘I’m going to do something here where the real mystery is not a who-done-it; it’s kind of a why-done-it or how-done-it.’ And I find that absolutely fascinating,” he says.

“And I can still sort of make myself shiver remembering the first time I realized what the twist of the story was and I still, to this day — and you wouldn’t believe how many times I’ve seen it on screen — I still get the same feeling when I watch it happen on screen.”

Wrestling it to screen was a singular task for Laurie, who’s best known here for acting roles in “The Night Manager,” “Veep,” “Catch-22,” and, of course, “House” (which earned him an Emmy nomination and two Screen Actors Awards).

“You probably need seven people to do the job of a director in the way that it really ought to be done,” he sighs.

“The calls upon your judgment and time and energy and stamina are almost infinite and the opportunity for making mistakes, likewise, is almost infinite,” he says.

But the source of both a director’s and an actor’s power lies in an underlying sense of truth, he says. “I think both actors and directors, they need to be people who watch people. They need to watch people and know instantly what is true and what isn’t. And it might be true in the way someone drinks a cup of tea. Or it might be true in the way someone conducts themselves in, I don’t know, a sword fight or rides a horse, or it may be in a 10-page dialogue scene at a graveside. It could be almost anything, but I think the audience generally has this instantaneous response: ‘I believe that, or I don’t. I respond to that, or I don’t.’ And I think both directors and actors need to be not just practiced at it, I think it needs to be an instinct in them both to watch people and to know when something isn’t right,” he says.

Something proved right for Laurie with “Why Didn’t They Ask Evans?” because of its sly wit, he says. “I always thought the novel had a kind of comic spirit to it. My theory is — and I've got no evidence for this ... but Agatha Christie published this novel a year after Dashiell Hammett published ‘The Thin Man.’ And I have it in my mind that she either read ‘The Thin Man,’ or she saw the film which came out the same year. And I think she was animated by that,” he says.

“It’s got a sort of ‘American’ bounce to it and a comic spirit, which I absolutely adored in ‘The Thin Man,’ too. And I've got a feeling that she did. And she wanted to imbue these characters with that kind of playfulness and spirit. And ultimately, it’s a kind of realism because people are funny,” he says.

“When I watch a film that has not a whisper of wit to it or humor ... it’s not that I'm disappointed by that absence, I just don't believe it as much because I think the way people respond to all kinds of things — fear, love, anger, all sorts of things — they very often resort to jokes as a way of processing those strong emotions. And I think that Agatha Christie deliberately set out to do something that had more of a comic spirit to it than perhaps some of her previous novels.”