Cobie Smulders Prepares Fans for Marvel's 'Secret Invasion' : 'It's Much More Dark in Tone' (Exclusive)

Marvel is continuing its Phase 5 rollout with the upcoming Disney+ series, Secret Invasion — and one of its stars, Cobie Smulders, is teasing what's to come.

Secret Invasion is the ninth television series in the Marvel Cinematic Universe (MCU). The show follows Samuel L. Jackson's Nick Fury as he learns a faction of Skrulls, an alien species previously seen in 2019's Captain Marvel, have invaded Earth. Joined by some of his allies, Fury and the gang race against time to stop the Skrulls in their tracks.

As for what fans can expect from the anticipated title, Smulders exclusively tells PEOPLE: "This series is much more dark in tone than ones previous. It's hard to know who to trust."

"Secret Invasion shows us insight into the lives of agents working to keep Earth and its inhabitants safe," Smulders, 41, continues. "Now, there is a major discovery of the Skrulls. Maria has been trying to get Nick Fury back to Earth to help with a multitude of problems but when the Skrulls become public knowledge, it finally gets his attention."

But Smulders also says that "with Marvel creating content for the streaming platform, we are able to spend more time with characters and get to know their backstories and deepen their relationships."

This new series sees the How I Met Your Mother alum return as Agent Maria Hill, which is a role she's helmed for over a decade.

"It's been an absolute dream to play Maria Hill for the last 10 years," she says. "She is a fantastic, multi-layered character who has triumphed over some intense moments in Marvel history."

As a reminder for fans who may have forgotten, Smulders points out that "the last time we saw Maria Hill on screen in Spider-Man: Far From Home, it was revealed in the end that she was a Skrull."

"So the audience is in the dark as to what she has been up to," she continues. "I'd like to think that she's been sipping Mai Tais on vacation somewhere after coming back from the Blip but most likely, she has been working on a mountain of backlogged issues."

Smulders has portrayed Maria Hill in several MCU projects, including The Avengers, Captain America: The Winter Soldier and Avengers: Age of Ultron.

With Secret Invasion, she gets to reunite on-screen with frequent costar Jackson. Ben Mendelsohn, Kingsley Ben-Adir, Emilia Clarke, Olivia Colman, Don Cheadle and Martin Freeman also star in the series.

Smulders says "the people" are the best part of being in the MCU.

"I have been so lucky to work with some of the most creative, talented and kind people in the business," she adds. "Also, my kids think I'm cool sometimes."

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Secret Invasion premieres June 21 on Disney+.