The upshot is to go to law (5)
I believe the answer is:
issue
'the upshot' is the definition.
(I've seen this in another clue)
'is to go to law' is the wordplay.
'to go to law' becomes 'sue' (as in suing somebody in court).
'is'+'sue'='ISSUE'
(Other definitions for issue that I've seen before include "One's offspring" , "Children; put out" , "Contentious subject" , "Important topic for debate" , "Important topic for offspring" .)