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. Early life Walker was born in Stepney in the East End of London and has an elder brother. She attended Saint Nicholas School at Old Harlow in Essex, and Forest School, Walthamstow, and undertook acting classes from the age of 12 in order to speak to boys. Interviewed in 2014 by The Daily Telegraph, she said, "I was really encouraged by my mother. My dad thought it was a ridiculous thing to do." Walker studied English at New Hall, Cambridge, becoming the first member of her family to go to university. She started her acting career with the Cambridge Footlights. Her contemporaries included Spooks writer David Wolstencroft and comedian Sue Perkins, who were all part of the 1990 national tour. Perkins, then an older undergraduate, was assigned to be her "college mother", although Walker later said: "She was the worst college mother I could have had. They're meant to hold your hand. She asked to borrow my bike, got drunk, and I never saw it again." Walker acted on stage as Perkins's stooge, and years later their partnership was resumed when Perkins cast Walker in her sitcom Heading Out. Career Offered a place at the Royal Academy of Dramatic Art on graduation from Cambridge, Walker already had some roles and an agent, so she decided to pursue her acting career. Based in London, she shared a flat with Perkins, Sarah Phelps, and Emma Kennedy, and acted at the Edinburgh Festival and the London Festival Fringe. Television Walker's first major television roles were in 1997, as Gypsy Jones in Channel 4's adaptation of A Dance to the Music of Time, and as English teacher Suzy Travis in two series of Steven Moffat's school-based sitcom Chalk. She has also appeared in guest roles in episodes of series such as Dalziel and Pascoe, Jonathan Creek, Pie