Wives and the third series of Scott & Bailey playing Helen Bartlett. In 2015, she appeared as Jackie "Stevie" Stevenson, the colleague of DI John River played by Stellan Skarsgård, in the BBC drama series River. Walker starred, alongside actor Sanjeev Bhaskar, in series one through four (2015–2021) of the ITV drama series Unforgotten as DCI Cassie Stuart. From 2018 to 2022 Walker starred as Hannah Defoe Stern, a divorce lawyer, in all three series of the BBC drama series The Split. Also in 2018, she played Reverend Jane Oliver in the BBC2 serial Collateral. Walker was number 10 on the "Radio Times TV 100" list for 2018, a list said to be determined by television executives and broadcasting veterans. In 2021, she starred in the British crime drama television series Annika, based on the BBC Radio 4 drama Annika Stranded, with Walker reprising the title role. Produced by Black Camel Pictures for Alibi and All3Media, the first episode aired on 17 August 2021. This is the eighth different police officer or detective role she has played on British TV. In 2022 Walker appeared in Stefan Golaszewski's drama, Marriage alongside Sean Bean. The series received mixed reviews from both critics and viewers. Theatre Walker won an Olivier Award in 2013 for Best Supporting Actress in her role as Judy, the main character Christopher's mother, in The Curious Incident of the Dog in the Night-Time. The play won seven Olivier Awards, equalling Matilda the Musical's record win in 2012. In 2014, she starred alongside Mark Strong and Phoebe Fox in Arthur Miller's play A View from the Bridge, at the Young Vic theatre. The play received extremely positive reviews from critics and transferred to Wyndham's Theatre in London's West End in 2015 and to the Lyceum Theatre on Broadway. In 2022 she starred as Miss Lily Moffat in the National Theatre revival in London of The Corn is Green, the 1938 autobiographical play by Emlyn Williams. Film In film, Walker's roles have tended to be smaller supporting parts. Her most prominent role was as one half of the folk duo in Four Weddings and a Funeral (1994), who sing "Can't Smile Without You" during the first church service. She also appeared in the feature film adaptation of the television series Thunderbirds (2004). In 2005, she portrayed a British journalist caught up in the Rwandan genocide in Shooting Dogs. Audio In 2002,