Ticket's about to go (6)
I believe the answer is:
return
'ticket's' is the definition.
(return ticket is a kind of ticket)
'about to go' is the wordplay.
'about' becomes 're' ('re' means regarding or about).
'to go' becomes 'turn' (as in one's go or turn in a game).
're'+'turn'='RETURN'
(Other definitions for return that I've seen before include "answer" , "Such a ticket brings you back" , "get back to original state" , "Take back" , "Come back with financial statement" .)