Horrible rogues turning on me (8)
I believe the answer is:
gruesome
'horrible' is the definition.
(I've seen this in another clue)
'rogues turning on me' is the wordplay.
'turning' indicates an anagram.
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'rogues' with letters rearranged gives 'grueso'.
'grueso'+'me'='GRUESOME'
(Other definitions for gruesome that I've seen before include "'Grisly, macabre (8)'" , "terrible" , "Revolting, filling one with horror and disgust" , "'Ghastly, grisly (8)'" , "Repulsive, horrid" .)