Is he to find out it's all over? (8)
I believe the answer is:
finished
'all over?' is the definition.
('finished' can be similar in meaning to 'all over')
'is he to find out' is the wordplay.
'to' is a charade indicator (letters next to each other).
'out' means one lot of letters goes inside another.
'is'+'he'='ishe'
'ishe' put inside 'find' is 'FINISHED'.
'it's' is the link.
(Other definitions for finished that I've seen before include "Done, over, ended" , "Ended. completed" , "exhausted" , "Brought to an end" , "wrapped up" .)