Happening in the Northern Territory on the day before (5)
I believe the answer is:
event
'happening' is the definition.
(I've seen this in other clues)
'northern territory on the day before' is the wordplay.
'northern territory' becomes 'nt'.
'on' is a charade indicator (letters next to each other).
'the day before' becomes 'eve' (eve is the night before something).
'nt' after 'eve' is 'EVENT'.
'in the' acts as a link.
(Other definitions for event that I've seen before include "Significant happening" , "Episode" , "A notable occurrence or happening" , "What will happen" , "High jump, say" .)