Soirée act arranged in highly specialised subjects (9)
I believe the answer is:
esoterica
'highly specialised subjects' is the definition.
(I've seen this before)
'soiree act arranged' is the wordplay.
'arranged' indicates anagramming the letters.
'soiree'+'act'='soireeact'
'soireeact' with letters rearranged gives 'ESOTERICA'.
'in' is the link.
(Other definitions for esoterica that I've seen before include "collection of specialist stuff" , "Mystic objects" , "Mysterious or secret things" , "Material appearing mysterious" , "narrow fields" .)