Get back again at three, with a girl (8)
I believe the answer is:
retrieve
'get back' is the definition.
(get back can mean to retrieve or recover)
'again at three with a girl' is the wordplay.
'again' becomes 're' (prefix meaning 'again').
'at' says to put letters next to each other.
'three' becomes 'tri' (prefix meaning 'three').
'with' means one lot of letters go next to another.
'a girl' becomes 'eve' ().
're'+'tri'+'eve'='RETRIEVE'
(Other definitions for retrieve that I've seen before include "Recover" , "Get or bring back something" , "Search for and discover" , "Win back" , "Regain or fetch" .)