Party with sister Ruby, perhaps, back in Australia? (4,5)
I believe the answer is:
down under
'in australia?' is the definition.
(I've seen this before)
'party with sister ruby perhaps back' is the wordplay.
'party' becomes 'do' (do is a kind of party).
'with' becomes 'w' (abbreviation**).
'sister' becomes 'nun' (I've seen this before).
'ruby perhaps' becomes 'red' (ruby is a kind of red).
'back' says the letters should be written backwards.
'red' written backwards gives 'der'.
'do'+'w'+'nun'+'der'='DOWN UNDER'
(Other definitions for down under that I've seen before include "In Oz, say?" , "Australia and/or New Zealand" , "Location of those in the Antipodes" , "Informal location of Australia" , "Far beneath, like Australia" .)