Nicola Jane Walker (born 15 May 1970) is an English actress, known for her starring roles in various British television programmes from the 1990s onwards, including that of Ruth Evershed in the spy drama Spooks (2003–2006 and 2009–2011) and DCI Cassie Stuart in Unforgotten (2015–2021). She has also worked in theatre, radio and film. She won the 2013 Olivier Award for Best Supporting Actress for the play The Curious Incident of the Dog in the Night-Time and was twice nominated for the BAFTA TV Award for Best Supporting Actress for the BBC drama Last Tango in Halifax. Her voice roles include Doctor Who companion Liv Chenka in various Big Finish audio plays (2011-present) and Eleanor Peck in The Lovecraft Investigations (2019-2020). Source: Wikipedia (en)