Set over the course of four days, the story centers on Detective Inspector Kip Glaspie (Mulligan), who refuses to accept that the murder is a random act of senseless violence and becomes determined to discover if there is a darker truth. Politician David Mars (Simm) instantly is embroiled in the drama through his turbulent relationship with his troubled and unpredictable ex, Karen (Piper). All the while, Jane Oliver (Walker), a compassionate vicar, struggles to conceal her affair with the only witness to the crime.