I want to talk about the two leads. You have this odd couple, the experienced detective who’s down on his luck and the eager younger constable. Can you talk about getting those actors on the same page? The tone they strike is specific, these sometimes tragic characters who are also goofballs by nature of their situation.

I think casting does a lot of the work. You need to find actors who instinctively have a sense for the material and how it should be played. And in some, in Saoirse in particular, they got that from pretty much day one. They understood how performance should function or could best function in this piece because you’ve got a world where it’s the world of the theater and it’s a period world, and it’s a murder mystery. There’s a danger that the performance can grow and becomes something theatrical in its own right. That actors end up playing the period in some way or playing the idea of these past whodunits that they’ve seen. And I was really clear that I thought the performances should be part of the thread that made this film clearly a contemporary piece. That they should have a contemporary comic tone to them. And that’s where Sam and Saoirse’s instincts lie. I think in general, and particularly in this piece, to trust that their writing will be funny if it’s played dead straight and they don’t need to excessively highlight the comedy in order to land it.

The movie has one foot in reality, since “The Mousetrap” is a real play and you have some characters who are actual people, like young Richard Attenborough. But it’s telling its own story. Can you talk about walking the line between reality and fantasy? Is this an alternate reality? 

That’s a great question. Part of the fun of the film, I think, is that it’s rooted in familiar elements of both the genre of the whodunit in terms of character tropes and the kind of devices that drive those stories. And also some real-life characters who [are] rooted in that time and place of 1953 London and specifically in the context of the West End theater land where the film’s based. And I think the balance was to not become a slave to … It’s not a faithful biopic. I hope that we’re coming to the characters who are real-life characters with love and respect.

And particularly in the case of Dicky Attenborough, that was certainly our intention. And it was something that [actor] Harris Dickinson and I talked about at the top, to what extent should this be informed by his real life? It was clear that this version of Dicky that we were presenting here was a quite specific type in as much as he’s the kind of actor who is always looking to inform his craft with observations of real people or the world that’s around him. He’s always looking to use a thing for his next great performance. And I think it was that side of the character that Harrison and I were both drawn to and to not get too bogged down in trying to tell the Richard Attenborough story, but hopefully presenting him in an affectionate light because he’s one of the greats.

There are a few obvious and not-so-obvious theatrical references in the dialogue. One character literally says “the play is the thing,” but worked into the dialogue. One character says “He’s a real hound, inspector,” a Tom Stoppard reference. Are there other little references in there?

[Writer Mark Chappell’s] script was dense with them and from memory, those ones you picked out are definitely key. One of my favorites, although not a direct reference, is when Sheila says, how would Agatha Christie-like it if someone took one of her stories and twisted it and manipulated it just for entertainment, which is very much just sort of hands up on our part. But in terms of deliberate or explicit references, when Mervyn says that unusual line when he is first on stage, when he says, “Is that the idea? Let the galled jade wince? Gather all the suspects and then interrogate each of us in turn until the mystery is solved?”

Well, the “galled jade wince” is the line from “Hamlet” and the play within the play in Hamlet is called “The Mousetrap.” That’s where the title for the Christie play [came from]. So you can see it all started to kind of eat of itself over time, but at the same time, it was important that you have those right things in the right balance. If there are too many, what feel like in-jokes, I think that pushes the audience away. You know what we wanted were these little Easter eggs for real fans of the genre or of these plays and books, but that if you miss it, no judgment. There’s plenty of other fun stuff to get involved in, if that makes sense.

“See How They Run” is in theaters now.