Psychotherapist Mia Cosgrove is having a bad week. Her beloved, motherly boss and mentor Judith has retired, she's recently moved into her fiance Patrick's cramped flat at the dodgy end of the Holloway Road and their wedding seems to always be over the horizon, both of them too busy to take the time out to plan it. Everything is in transition. All of this pales into insignificance when she receives a call from her oldest friend, Lysette. A young mum Lysette was close to has died in mysterious circumstances: Sarah Bell's crumpled body was found at the bottom of a multi-storey car park, a text message saying 'I'm so sorry' with a single X on her phone, left unsent and unaddressed. Mia races home to offer support, but as the situation grows ever darker, all of her vows to never get involved in another criminal case start to crumble.