When you’re a secret agent about to kill people, be sure to wear a helmet. (Paramount Pictures)

When Ethan Hunt and Ilsa Faust reunite in “Mission: Impossible — Fallout,” he’s surprised. He thought she had gotten out of the spy game.

She hasn’t.

The former MI6 agent, played by Rebecca Ferguson (“The Greatest Showman”), is back and just as badass as ever.

“She is who she is, and that’s why I love her,” Ferguson says. “She has an agenda and a motive that’s changed, [but] it’s not like she’s going through character development per se. She is an equal to Ethan Hunt and stays that way through this film.”

“Fallout,” opening tonight, is what you’d expect a “Mission: Impossible” movie to be. Hunt, the superspy played by Tom Cruise for 22 years now, leads a secret squad to take down some anarchist bad guys who have, unfortunately, gotten ahold of some atomic bombs. Ilsa isn’t part of the team; she has a mysterious ulterior motive that’s best not spoiled. One thing that hasn’t changed from 2015’s “Mission: Impossible — Rogue Nation,” the film that introduced Ferguson’s character, is that her relationship with Ethan is still complicated.

“I think their working relationship finds deeper ground in this one,” Ferguson says. “Ethan, I think, is gradually questioning his agenda; I think that humanizes him in many ways. And also, Ilsa has to sit down and think, ‘Why am I doing this? What am I doing it for, and what are the consequences I’m willing to face?’”

While Ethan and Ilsa grapple with these issues, they’re often grappling with each other, too.
“I love the idea that they’ll run over each other. Literally, they’ll run over each other to get what they want,” Ferguson says. “They will also protect each other and save each other’s lives without hesitation, so there are these emotions constantly bubbling.”

Ilsa may find herself in danger, but she is never a damsel in distress. Neither are any of the other female characters, including ever-suspicious CIA chief Erica Sloan (Angela Bassett) and a femme fatale known as the White Widow (Vanessa Kirby), both of whom play pivotal roles in the story.

Ferguson credits returning writer-director Christopher McQuarrie for the movie’s deep bench of vital players.

“Chris is very particular with the necessity of a character in a film,” she says. “If you would take out any of the characters — not just the women — there would be a massive hole in the script. And that’s equality, isn’t it?”