Ruin party at country club? (4)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
undo
'ruin' is the definition.
(someone's undoing is their ruin)
'party at country club?' is the wordplay.
'party' becomes 'do' (do can informally mean a party).
'at' says to put letters next to each other (I've seen this in other clues).
'country club?' becomes 'UN' (United Nations, group of countries).
'do' after 'un' is 'UNDO'.
(Other definitions for undo that I've seen before include "Cancel -- annul -- reverse" , "Loosen; annul" , "Relax" , "Bring to nought" , "Ruin, destroy" .)