DI Helen Morton (Caroline Catz) does not appear in Peter Robinson's original novels. She was introduced in Series 2 as a temporary replacement for DS Annie Cabbot (Andrea Lowe) who took maternity leave because Andrea Lowe was pregnant in real life. Helen (Caroline) stayed for the last three seasons.
Caroline Catz also played a DI in Murder In Suburbia (DI Kate "Ash" Ashurst).
Caroline Catz first played a member of a police force when she was cast in The Bill as PC Rosie Fox from 1998-2000. She also starred in The Vice from 1999 to 2003 as PC Cheryl Hutchins.
This is the fourth series in which Caroline Catz has played a cop.