The chapter draws upon a critical realist analysis to demonstrate recent changes in the UK Middle Market of Class A drugs and responses to them. The chapter contends that previous definitions of the "middle market" specified from agencies charged with disruption have overly relied upon definitions which best suit the professionals involved to the detriment of young and vulnerable people caught up in what has become known as County lines. The chapter provides a new analysis of this part of the distribution network and discusses criminal exploitation and transitions of some street gangs to local organised crime networks.