Exclusive story second on supermarket (5)
I believe the answer is:
scoop
'exclusive story' is the definition.
(I've seen this in another clue)
'second on supermarket' is the wordplay.
'second' becomes 's' (common abbreviation).
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'supermarket' becomes 'Co-op' (The Co-operative).
's'+'coop'='SCOOP'
(Other definitions for scoop that I've seen before include "Reporting exclusive" , "Find utensil" , "Implement for ice cream" , "Waugh novel; some ice-cream" , "Haul" .)