Left in dark (8)
I believe the answer is:
sinister
I believe this clue is a double definition.
'left' is the first definition.
(thesaurus)
'dark' is the second definition.
(thesaurus)
'in' is the link.
(Other definitions for sinister that I've seen before include "On the left (of shield) (her.); wicked, criminal" , "Spooky" , "Threatening evil on the heraldic left" , "Suggestive of evil, to the left in heraldry" , "Very unpleasant" .)