One between parties in awfully nice resorts (11)
I believe the answer is:
intercessor
'one between parties' is the definition.
(someone who mediates between parties)
'awfully nice resorts' is the wordplay.
'awfully' indicates an anagram.
'nice'+'resorts'='niceresorts'
'niceresorts' anagrammed gives 'INTERCESSOR'.
'in' is the link.
(Other definitions for intercessor that I've seen before include "one steps in to help" , "One who mediates" .)