Possible Clues:

• It's a party, so lay back
• Neighbourly get-together
• Government assistance for party planners?
• Party like this shall be heard!
• Convivial - party
• Of society or its organisation
• See 8
• Party of American spies in French sun
• 15, say, for production of 'Cosi' (gala performance) with Wagner's work
• Do true spies leave the merest trace?