Even though Alison McCosh was involved with the production of Netflix‘s “Peaky Blinders” for the series’ last three season, returning for the show’s final chapter was a “very different” beast. “When we did [Seasons] Four, Five and Six, it was mostly about the family and ensemble cast. But it felt like this was one man’s journey,” the costume designer said of working on “Peaky Blinders: The Immortal Man.” “That took a different turn for us. Obviously, it’s a bigger scale. It was certainly very different.”

McCosh spoke with WWD about the film, out on Netflix, and how she and her team adapted to a new time period in English history, introduced new characters to the “Peaky Blinders” universe and the moment in the script that shook her most.

“Peaky Blinders: The Immortal Man” follows Tommy Shelby, played by “Oppenheimer” Oscar-winner Cillian Murphy, as he’s dragged back into the world of the Peaky Blinders gang when his son Duke, played by Barry Keoghan, makes a deal to tip the scales of World War II in the Nazi regime’s favor.

The film leaves the 1920s and 1930s behind for the war-torn 1940s. “We had a lot of reference around Birmingham and what that looked like on the streets and people on the streets. It was a very interesting time for us to look at,” McCosh said, referencing the state of the English city that was heavily bombed during World War II. The costume designer and her team used photos to build a better understanding of the next chapter in the “Peaky Blinders” saga. But some costuming was far more idiosyncratic.

“Dune” star Rebecca Ferguson enters the “Peaky Blinders” universe as Kaulo, a mysterious figure who holds ties to Tommy’s past. A character with Romani background and elements of supernatural, Kaulo merged both past and present. “We looked at quite a few references across the board. We took from some modern images, we took from period images, we sort of meshed that together,” said McCosh. Known for its use of anachronistic music, “Peaky Blinders” has a tendency to merge history with contemporary details.

Ferguson’s coat, however, was “an original piece that we managed to bring back to life. At first, we thought about remaking it. But the beauty of it inside, we felt needed to live on.” McCosh and her team “dyed it and just brought it back to life. So we thought, why not use the original piece because it drapes so beautifully on her.” References to the series, like Ferguson’s boots — “kind of reminiscent of what Polly used to wear” — paid homage to the late actress Helen McCrory who played Polly Gray.

Apart from new additions Ferguson and Keoghan to the “Peaky Blinders” world, other returning actors include Sophie Rundle, who plays Tommy’s sister Ada, wears one of the most significant costumes from the film. “As a costume designer, we’re there to interpret the script and what that means in a visual story,” McCosh said, recalling how a sequence involving Rundle’s character gave the costume designer “goosebumps.”

McCosh was determined to give Rundle a “moment of color and of power,” and costuming was the ideal avenue. The costume designer crafted a vibrant violet coat from “an original fabric that we then had dipped and hand dyed,” she said, adding, “you can see in the front of the panels a little deeper in color into the sleeve, and [the] skirt is a little different.”

“We went through different tones and really thought about that carefully,” McCosh said, emphasizing the importance of seeing Ada in “some sort of vibrancy.”

McCosh has been immersed in the “Peaky Blinders” world for roughly a decade, but it was when she and series’ star Cillian Murphy worked together on the 2024 film “Small Things Like These” that the idea of a film as the final punctuation on the show felt like the proper send-off to the series.

“I remember when we were doing Season Six and we thought that was a finale and that was it. And then Cillian and I were working on another project together. We were just talking about it, and it felt right to do it. It felt like we had to close that chapter. Both of us felt the same way about it — that there was another story to tell,” McCosh said. “I’m very grateful for that, for the journey of being with ‘Peaky Blinders.’”

“Peaky Blinders: The Immortal Man” and the “Peaky Blinders” series are available to stream on Netflix.