Detective who follows a trail (6)
I believe the answer is:
sleuth
'detective who follows a trail' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for sleuth that I've seen before include "Follow" , "Bloodhound" , "Sherlock Holmes, for example" , "A detective like Sherlock - given to hustle" , "Private eye" .)