For anyone who’s seen Sonya Cassidy’s blazing turn as DEA Agent Susan Duffy opposite Alan Ritchson in Reacher Season 3, it would be easy to think that she was born and bred in South Boston.

In truth, however, Cassidy is a native of the U.K., where since 2009 she’s been honing her acting craft on various British films and TV shows. Cassidy has also starred in U.S. productions like the comedy mystery series Lodge 49, but with Reacher, she’s truly arrived on U.S. television with such a tremendous force that you’ll feel like you’re about to get your butt kicked every time Duffy speaks.

In a recent Zoom conversation about Reacher Season 3, Cassidy said that she dove into virtual conversations with residents of the East Coast and studied the accents of others to help find Duffy’s voice.

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“I live in London, so it was a little ways for me to travel, so I hung out with as many Bostonians as I could through the portal that is the internet and finding old interviews,” Cassidy recalled for me. “There’s some great old Boston Globe interviews, like when Whitey Bulger was caught, and others with some old Boston longshoremen, who have got quite strong accents.

“I looked at those to get my muscles around the accent, to just hear it in a heightened form," Cassidy added. "Then I worked with a dialect coach to soften the edges a bit. But, yeah, I watched as much as I could in order to absorb it.”

In Reacher Season 3, which is new on Prime Video, Cassidy’s Agent Duffy recruits Reacher (Ritchson) to infiltrate the inner workings of a shady business magnate, Zachary Beck (Anthony Michael Hall), who is purportedly in the business of importing rugs.

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Duffy, though, suspects that drugs are somehow involved in Beck’s business dealings, but in order to prove it, the Drug Enforcement Agency agent needs Reacher on the inside. Reacher, in turn, agrees to take part in Duffy’s operation since an old adversary, Xavier Quinn (Brian Tee) is tied into Beck’s criminal organization and the undercover assignment gives the former Army Military Police investigator his best shot of getting to the person responsible for a deep personal tragedy.

For Cassidy, becoming Duffy was more than just learning an accent to play the no-BS DEA agent—it was bringing the essence of a seasoned, salty-tongued Southie to the role. After all, Duffy is a character who has no qualms about calling Reacher an a—hole to his face and smacking around a potential informant with a book when he’s non-cooperative—and that’s just for starters.

“It was really about getting a hook for the character. It’s always about so much more than she sounds. It’s a psychology. It’s a culture," Cassidy explained. "None of what Duffy says would sound right in my accent. She's cooler than I will ever be!”

Sonya Cassidy said Reacher was very much on her radar before the opportunity came up to play DEA Agent Susan Duffy in Season 3 because she was such a big fan of Reacher seasons 1 and 2.

On top of the character’s sharp dialogue and “Don’t mess with me” attitude, Cassidy was thrilled to play Duffy because the season—thanks to the nuanced source material from author Lee Child , as well as the the work of Reacher creator Nick Santora and executive producer Don Granger—delves into a backstory that her character is haunted by.

Yes, there’s plenty of action and heightened stakes the characters face, Cassidy said, but not to the point where it takes precedence over any character’s crucial backstories—including Duffy and her personal motivation behind putting Reacher in harm’s way.

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“What Nick and the amazing writing team has done is take [that backstory] and bring it into the show … in particular with the female characters, who have much more agency and more of a sense of themselves,” Cassidy explained. "They have their own nuance of what they bring to the show along with the testosterone [that drives it]. It’s really exciting to watch and only enriches the series even more.

“What’s lovely about Season 3 is it really hits the ground running with Duffy. I think we’re actually seeing Duffy’s critical life and career moments happen in real-time,” Cassidy added. “So, while we get more from Reacher in terms of his flashbacks, I feel like we’re getting Duffy’s moments, too. It is so dangerous. [The situation has] gone so much further than she ever could have imagined.”

In a separate Zoom conversation, Jack Reacher author Lee Child said he loved writing the character of Susan Duffy for Persuader, which is the novel Reacher Season 3 is based upon.

However, the euphoria that Child said he experienced creating Duffy for the book ended up being a bittersweet experience—which he was reminded of after seeing Sonya Cassidy bring the character to life with such vibrance in Reacher Season 3.

In short, Child said, Duffy is a character that you can’t help but fall in love with—this writer certainly did—which makes it tough when it’s time for Jack Reacher to move on to a new city and a new adventure in the next novel.

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“I get exactly what you just said, that you fell in love with her. I do that with every book,” Child told me. “There is a different woman in every book and I'm hopelessly in love with them and I'm bitterly disappointed when the book finishes and I have to leave them.

“That’s how it works, though … All three seasons have had an outstanding love interest and Duffy is that [in Season 3]. I love how she’s a rough, tough badass,” Child added. “I remember writing that book and being so sad that I would never see her again.”

The first three episodes of Reacher Season 3 are streaming exclusively on Prime Video, with new episodes dropping every Thursday through March 27.

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