When the hunt for the female assassin who killed his sister proves futile, King returns to MI5 where he is propositioned by a secretive organisation headed by a familiar face. King takes on both the Russian intelligence services and organised crime to halt them bypassing sanctions and flooding the UK market with forged sovereigns cast from seized Nazi gold in a bid to sink Britain's economy.

Meanwhile in Marseilles Caroline Darby is hunting the same assassin who killed her aunt and attacked her parents. With King fighting on another front, the team backs her up but they soon discover that the CIA have an interest in their quarry. The race is on to catch a killer before she finds help from an unexpected source.

King closes in on the forging operation in Estonia but doesn't know who to trust as the parameters of the operation change, and he realises that he should never have left Caroline in France, hoping he is not too late before the assassin closes in.