`Collateral' is a four-part thriller set in London that takes place over four days. When a pizza delivery driver is shot down in South London, Detective Inspector Kip Glaspie, played by `Great Gatsby' star Carey Mulligan, is left in charge of the investigation and refuses to accept the murder as just a random act of violence. As she investigates, she soon finds herself being drawn into the darker side of underworld London. At the same time, politician David Mars, played by John Simm, becomes embroiled in the events due to his rocky relationship with his unpredictable ex, Karen, and a vicar struggles to conceal her affair with the only witness to the shooting. Disparate worlds collide and become entangled as the investigation develops.