Cate Blanchett Shares What Gave Her ‘Low-Level Anxiety’ Making Black Bag with Michael Fassbender (Exclusive)

In the new espionage thriller Black Bag, Cate Blanchett and Michael Fassbender play Kathryn St. Jean and George Woodhouse, married British spies who aren’t always honest with each other out of necessity. 

With national security information at stake, keeping secrets is just part of the job. Even something as seemingly simple as the location of a business trip may be off limits for discussion — those topics are referred to as being in the so-called “black bag.”

When George is tasked with finding out who at the National Cyber Security Centre is a potential traitor, he looks into several coworkers, played by Regé-Jean Page, Naomie Harris, Marisa Abela and Tom Burke. His own wife is on the list too.

“The weird thing about these characters is they work so closely with one another, and so they know operationally so much about one another and have a lot of information on one another, but yet they don't actually know what's going on with each other,” Blanchett, 55, tells PEOPLE.

“There's an interiority to the characters that they have no idea about, no matter how many high stakes operations they've been involved in together, which is a very weird thing to play,” she continues.

Two pivotal dinner party scenes — during which George gets a close-up look at the people he’s investigating — take place in the Woodhouse-St. Jean home, a spectacular residence with a glass-walled garden just off the dining room.

In the center is what Blanchett calls a “beautiful tree, which is totally enclosed in glass,” as envisioned by production designer Phil Messina. “It’s very subtle in the background.”

“So it seemed to me a metaphor about the way they all lived their lives is that there was so much life, but it was entrapped,” says Blanchett. 

Metaphors aside, “I had low-level anxiety for the health of the tree,” quips Blanchett.

The set — built at Pinewood Studios in England — was incredibly realistic and felt like a true home, adds Fassbender. 

“We had a full house to walk around in,” he says. “You go up the stairs into the bedroom and our wardrobe-bathroom area — it was all built. And various people on the crew were like, ‘Oh, I want to take that oven and table and chairs.’ It was so beautifully designed.”

Black Bag is in theaters March 14.