Fiddling emperor in north-east or heading north (4)
I believe the answer is:
nero
'fiddling emperor' is the definition.
(emperor who supposedly fiddled as Rome burned)
'north-east or heading north' is the wordplay.
'north east' becomes 'ne'.
'heading north' shows that the letters should be reversed in order (in a down clue, letters travel north).
'or' in reverse letter order is 'ro'.
'ne'+'ro'='NERO'
'in' is the link.
(Other definitions for nero that I've seen before include "Roman tyrant" , "Emperor, 'burnt' Rome" , "He's reputed to have fiddled while Rome burned" , "He's reported to have fiddled while Rome burned" , "Emperor said to have started the fire that destroyed Rome" .)