Chief Superintendent Jackie Starling is a ruthless, ambitious, senior officer in the UK National Crime Agency. Tasked with closing down the "County Lines" drug dealers she is determined to get a result; whatever it takes.

Catching and convicting the dealers is easy enough; most of them are children. But these results are temporary and the young criminals are replaced within days. Starling needs a different strategy and so faces a choice: Stay within the rules and chip away at the foot soldiers or kill the bosses? She decides to go for the bosses.

She knows someone capable of carrying out the tasks ahead and she has the power to persuade him to deliver. But Starling has no idea what they will be up against or the prospect of a horrifying death that she will be facing.

"County Lines" is the UK distribution model that involves urban gangs expanding their markets for crack cocaine and heroin into smaller towns by setting up phone lines through which they sell the Class A drugs.