Charlie Cooper gained a new appreciation for the "mathematical" precision of a great whodunnit story while appearing in the 1950s-set thriller See How They Run.

The This Country actor plays theatre usher Dennis in the new murder-mystery, which is set amid the glamour of a West End production of Agatha Christie's classic thriller The Mousetrap.

The discovery of a dead body behind the scenes causes the roulette wheel of potential suspects to spin, while cops played by Sam Rockwell and Saoirse Ronan aim to track down the killer.

"The challenge is with the writers, I think. It's so formulaic, isn't it — a murder-mystery?" Cooper told Yahoo.

See How They Run hits UK cinemas on 9 September.

Video transcript

TOM BUTLER: I guess it must be an interesting challenge as an actor, because every actor who's in this has to appear suspicious.

CHARLIE COOPER: Yeah, totally. Well, I think it's less so with the actors. The more challenge is with the writer, I think, because it's like so-- it's so formulaic, isn't it, murder mysteries? And you've got to pitch it just perfectly. It's sort of like-- so mathematical, isn't it? If you linger on a character for too long in one scene you can sort of-- you know, it's sort of a red herring or whatever.

And so the way it was constructed and written was really meticulous. And so as an actor, you don't have to actually do much. You just do what's on the page. And luckily-- and it's all there.

TOM BUTLER: It's that balance, isn't it, of giving all of the information the audience needs to work it out--

CHARLIE COOPER: Yeah.

TOM BUTLER: But not so much information that it's obvious.

CHARLIE COOPER: Definitely. Because I'm really bad at knowing who.

TOM BUTLER: Oh, me too. I never get it.

CHARLIE COOPER: Some people just get it. My girlfriend gets it straight away. I'm just like, oh, just shut up. [INAUDIBLE] the thing.

But that's the thing. I think, again with this, it's like, just go with the ride. Enjoy it. And don't try and guess too soon, I think would be my advice.