Detective Inspector Karen Lacy is a plaincloth officer with the Metropolitain Police Counter Terrorism Unit, she first appeared in 2008 following the death of PC Emma Keane in the series of frontline episodes. Then she returned again in 2009 as a Intelligence officer Serious Organised Crime Agency (SOCA) to investigate the Monks family were DS Max Carter was undercover.

D.I. Karen Lacy with D.C. Mickey Webb.
since then she has not returned.
she is portrayed by english actress Elizabeth May Brice