There was obviously a lot of research involved in writing a complex thriller like Black Bag, especially when it comes to figuring out the inner workings of an agency where much of its activities are so top secret, they're referred to as "black bag" i.e. need-to-know. While talking covertly to operatives to prepare his Mission: Impossible script, David Koepp began to dig deeper into their personal lives during his confidential interviews. Speaking with Cinema Daily US recently, Koepp explained that he was doing research for what would become a very different action-driven spy thriller when he learned more about how couples in the field work together. “I would start asking about people's personal lives, because it struck me that a profession where you lie for a living has to be a hard one to have personal relationships in," he said in the interview. "To a person, they would say, ‘Yeah, it's brutal. It's a real conundrum.’ The line actually showed up in Black Bag: ‘If I date someone outside the community, they don't understand, and they don't have any clearance, so I can't talk about anything. And if I date someone inside the community, I don't trust them, because they're liars, and so am I.’ I just kind of carried that nugget in my head as an approach to a spy movie I haven't seen before, and I'd like to see it.”

Other aspects of the film, such as George's proclivity for fishing, also came out of Koepp's later research, once he discovered that a legendary CIA spy named James Jesus Angleton enjoyed bass fishing. That seemed like it might be relevant to George's occupation, as he spends his time fishing for the truth, but that was just a tangential tidbit Koepp put into his script, as he kept exploring some of the problems that might arise when couples, married or otherwise, work together in any capacity. Those problems are frequently on display in Black Bag, as some of the players around George and Kathryn begin revealing their own indiscretions, often with each other, leading to moments that go far beyond merely being awkward.

Although the initial idea for Black Bag was in Koepp's head back in the mid-'90s, he struggled to get around to writing it, especially as other movies came along that seemingly explored the same topic, although in a very different way than his film. “I keep a lot of script ideas in various files," Koepp has admitted. "I was going to work on it, and then True Lies came out, the James Cameron movie, and they're married. And I thought, ‘Oh, well, that kind of steals my area.’ And then I was going to work on it again, and Mr. and Mrs. Smith came out. Then I realized that marriage is a common institution; I don't think I have to wait.” It took two unplanned breaks in the industry, the COVID pandemic and the writers' strike, to finally give Koepp the opportunity to sit down and flesh out his earlier idea into a full script.

Watching Black Bag, I was struck by a moment from a scene in which Michael Fassbender's spy goes fishing. Out on the water, he finds it an ideal place to think, and he begins recalling the dinner he'd hosted the night before, which he'd designed to fish out a rat among fellow spies, including his wife, played by Cate Blanchett. The film here reminds of the great scene in De Palma's Mission: Impossible where Jim Phelps has made contact with Ethan Hunt in London. Over coffee, Ethan begins flashing back to the disastrous night in Prague, and, despite Ethan's words to Phelps, we see things either as Ethan remembers them, or as Ethan believes they likely happened. Of course, Ethan finds it too painful to believe the truth about Claire, and closes his eyes and tries to wipe the thought from his mind, inventing an alternative scenario that he struggles to accept.

There is a similar echo of that moment in the Black Bag fishing scene. As Fassbender's George Woodhouse remembers each face from the dinner the night before, staring back at him, the montage of faces ends by lingering on Blanchett, and then cuts back to George in the fishing boat, closing his eyes, apparently pained by the thought of even considering her as the culprit.