From Wales comes Thursday’s “Death Valley,” BritBox’s latest comically inclined crime-solving duo.

Naturally, they’re an engaging if slightly odd couple. John Chapel (Timothy Spall) is a retired actor, still admired (and recognized) as the star of “Caesar,” a detective series.

He’s (unofficially) recruited by the young Welsh Detective Sergeant Janie Mallowan (Gwyneth Keyworth) who is gob-smacked to meet her favorite TV detective and sees that his on-the-job acting has made him a valuable cohort.

Spall, among England’s most revered actors, has a ball sending up thespian pretention. Janie doesn’t even try to be fake blasé when they meet.

“You can tell exactly what she’s thinking by her face,” Keyworth, 34, acknowledged from the UK on a video interview. “She literally can be read like an open book.”

Keyworth is a classically trained Royal Academy of Dramatic Art grad who starred as Scout in the West End’s “To Kill a Mockingbird” with Rafe Spall as Atticus Finch (yes, Timothy’s son).

She felt an instant affinity for Janie Mallowan. “When I read the part I was, ‘This feels like I’m meant to do it.’

At the start of the series, Janie’s shut down her personal life as a way to hide from grief. “Literally, in the first episode, she talks about grief as something you put away and store in the attic: Just don’t think about it.

“But as we know with life, you can’t do that. Through her friendship with John Chapel she rediscovers her own emotional sense of self.”

There’s comedy in Janie being a “Caesar” fan, having watched every episode. “It’s been her comfort blanket. A show like ‘Gilmore Girls,’ that they’ll just watch over and over.

“When she meets John Chapel, she hasn’t quite linked that he is the guy from the show she’s spent many hours with. Yet there’s a part of her brain that goes, ‘He’s a stranger and actually, you should be doing a job,’ and part of her brain that goes, ‘Oh. My. God. It’s your hero.’

“And he completely overtakes her, which she does learn to regret somewhat as the series goes on and John Chapel keeps intruding on her cases. It becomes a really funny dynamic.

“And, yes, she lives with her mom. A large part of that is it’s a bit of an excuse for Janie who hasn’t completely got the skills to live on her own yet.

“Because she’s still not well. She hasn’t grieved her best friend’s death. So in her professional life, she’s at the top of her game. But in her personal life, she’s a bit of a teenager.”

BritBox streams the first two episodes of “Death Valley” May 29