Party including a show (6)
I believe the answer is:
reveal
'show' is the definition.
(I know that reveal is a more specific form of the action show)
'party including a' is the wordplay.
'party' becomes 'revel' (I've seen this in another clue).
'including' indicates putting letters inside.
'revel' going around 'a' is 'REVEAL'.
(Other definitions for reveal that I've seen before include "Leaver (anag.)" , "Final disclosure" , "Open up" , "Disclose, make apparent" , "Remove cover, unveil" .)