Why did Nicola Walker leave Unforgotten as DCI Cassie Stuart?

Why did Nicola Walker leave Unforgotten? Nicola Walker as DCI Cassie Stuart in Unforgotten.
Unforgotten star Nicola Walker as DCI Cassie Stuart. (Image credit: ITV)

Nicola Walker was a fan favourite in Unforgotten, where she played the leading role of DCI Cassie Stuart opposite Sanjeev Bhaskar's DI Sunil "Sunny" Khan.

However, DCI Stuart won't be returning for Unforgotten season 5, following the shocking ending of season 4 where she was killed off in a horrific road accident. Naturally, her death has devastated those around her and her loss will still be hanging over Sunny in upcoming episodes.

In the new season, Sunny will have a new detective partner in DCI Jessica James (Sinéad Keenan) who will step in to help him with the investigations going forward. 

But why did Nicola Walker leave Unforgotten? Here's what you need to know about her departure from the hit ITV drama.

Why did Nicola Walker leave Unforgotten?

Although Nicola Walker was a fan favourite, it seems her departure from the series was planned for a long time and that everyone had agreed it was the right decision. 

In an interview with TV Insider, Nicola Walker and series creator Chris Lang explained why Cassie's character was killed off in the devastating season 4 finale, which ended on her funeral.

Nicola said: "We were talking from the beginning, really, about what he was doing with this character and this story he wanted to tell. Chris and I were always interested in looking at the cost of being involved with these sorts of cases that we all love watching on television. Cassie does not have superpowers. She’s an ordinary person who’s really good at her job and it took her to the place of having an emotional breakdown."

Unforgotten stars Nicola Walker and Sanjeev Bhaskar

DI Sunil "Sunny" Khan and DCI Cassie Stuart worked together on a number of cases. (Image credit: ITV)

She added: "We talked a lot after season 3 about where it was going to go, and it was a joint decision. I think the clues were there in season 3. The title of the show is Unforgotten and I think there’s a great deal of narrative beauty to this woman. She’s not going to be forgotten. I felt like she was quietly very unusual on television because she was a real person."

So while it's sad that Nicola Walker has left the series, those involved in Unforgotten knew it was coming for a little while and they have felt that Cassie's story has run its course and it's time to focus on new characters and plotlines.

Who is Sinéad Keenan?

Unforgotten season 5 arrives on ITVX in 2023.

DI Sunil "Sunny" Khan will work with newcomer DCI Jessica James following Cassie's death. (Image credit: ITV)

Sinéad Keenan is an Irish actress who has worked in television, film and stage. She is best known for her roles as Nina in the BBC drama Being Human and Theresa Ryan in the mini-series Three Families.

She recently had a cameo appearance in Channel 4's Derry Girls where she played Aideen, an old school friend of Ma Mary and Sarah who they couldn't remember!

Her Unforgotten character is DCI Jessica James, and apparently she doesn't really get on well with Sunny to begin with. Sinéad told Radio Times: "When they meet, it is loggerheads. It’s passive-aggressive, jibes, in a way it’s jostling for position.

"It’s not until episode four, once the shock of her news dissipates a bit, that she really tries to get herself together. And we hope they can start working together as opposed to beside each other."

Unforgotten returns to ITV1 on Monday, February 27 at 9 pm. Episodes are also available on ITVX

Lucy Buglass
Senior Staff Writer

Lucy joined the WhatToWatch.com team in 2021, where she writes series guides for must-watch programmes, reviews and the latest TV news. Originally from Northumberland, she graduated from Oxford Brookes University with a degree in Film Studies and moved to London to begin a career writing about entertainment.


She is a Rotten Tomatoes approved film critic and has a huge passion for cinema. She especially loves horror, thriller and anything crime-related. Her favourite TV programmes include Inside No 9, American Horror Story, Stranger Things and Black Mirror but she is also partial to a quiz show or a bit of Say Yes to the Dress