Ninety featuring in subtle story published only by us (9)
I believe the answer is:
exclusive
'story published only by us' is the definition.
(as in a newspaper exclusive)
'ninety featuring in subtle' is the wordplay.
'ninety' becomes 'XC' (Roman numerals).
'featuring in' indicates putting letters inside.
'subtle' becomes 'elusive' (subtle can mean elusive or finely drawn).
'xc' placed inside 'elusive' is 'EXCLUSIVE'.
(Other definitions for exclusive that I've seen before include "Select, high-class" , "Not divided or shared with others" , "article kept away from other rags" , "Catering for only the wealthy, not obtainable elsewhere" , "choice" .)