Sadie is an ambitious and successful undercover police officer. After playing the key role in a major drug bust she is dismissed by her male colleagues. And then she's suddenly given the chance to work on a case that could make her career.

Enters the world of Colin Stagg, the Met Police's prime suspect. In officers' minds, Stagg perfectly fitted the criminal profile of the killer, and yet there was no hard evidence linking him to the murder. Their hopes of a conviction rested on the involvement of undercover officer Sadie Byrne in his life.

As the weeks pass, undercover police officer Sadie - aka Lizzie - is unable to crack prime suspect Colin Stagg, and it soon becomes clear that the pressure she's under is starting to have a profound impact.

Colin Stagg is interrogated by police about Rachel's murder details and is subsequently put on trial.