Grace, providing service at a party (5)
I believe the answer is:
adorn
'grace' is the definition.
('adorn' can be a synonym of 'grace')
'service at a party' is the wordplay.
'service' becomes 'rn' (abbreviation for Royal Navy).
'at' is a charade indicator (letters next to each other) (I've seen this in other clues).
'party' becomes 'do' (do is a kind of party).
'a'+'do'='ado'
'rn' put after 'ado' is 'ADORN'.
'providing' is the link.
(Other definitions for adorn that I've seen before include "Embellish, decorate" , "Festoon" , "Attire" , "Make more attractive" , "dress" .)