Newly promoted to Detective Inspector, William Warwick is tasked with a dangerous new line of work, to go undercover and expose crime of another kind - corruption at the heart of the Metropolitan Police Force. Along with detectives Rebecca Pankhurst and Nicky Bailey, his team is focused on following Detective Jerry Summers, a young officer whose lifestyle exceeds his income. But the investigation risks being compromised when Nicky falls for Summers.

Meanwhile, notorious drug baron Ahmed Rashidi goes on trial, while William's father Sir Julian and sister Grace lead the prosecution case. William's wife Beth, now a new mother to twins, makes a surprising new friend in Christina Faulkner - who has not only turned over a new leaf, but also has a new-found source of income when Faulkner dies suddenly of a heart attack and she stands to be sole inheritor of his estate.

As the undercover officers draws the threads together, William realises that the corruption may go deeper still and more of his colleagues might be willing to turn a blind eye.