Party in which to see upper-class couple (3)
I believe the answer is:
duo
'couple' is the definition.
('duo' can be a synonym of 'couple')
'party in which to see upper-class' is the wordplay.
'party' becomes 'do' (do is a kind of party).
'in which to see' indicates putting letters inside.
'upper-class' becomes 'u' ('u' can be similar in meaning to 'upper-class').
'do' enclosing 'u' is 'DUO'.
(Other definitions for duo that I've seen before include "Pair (of people, things)" , "Pair of singers" , "Double act" , "entertainers such as Eric and Ernie" , "Brace" .)