DCI Erin Gray (played by Nikki Amuka-Bird) is a new member of the team in Series 2. She is highly intelligent and ambitious, but young and naive, having come from a sheltered background. She makes it clear in Season two, episode 1 that she doesn't want her name tarnished like Ripley's, and she keeps her distance from Luther. Luther keeps her on because she is newly qualified and good at her job. Having become convinced that Luther is dirty, she attempts to find evidence of this during Series 2, but Ripley eliminates the evidence to protect Luther.
Without evidence, her complaints about Luther smear her career, and she leaves the Serious and Serial Unit. Between Series 2 and 3 she joins a unit investigating police corruption, and is promoted to Detective Chief Inspector. During Series 3, she is working with Detective Superintendent George Stark in an investigation against Luther and is last seen being taken to hospital following an attack from the vigilante killer Tom Marwood