Work out alone — very into that (5)
I believe the answer is:
solve
'work out alone very into that' is the definition.
'solve' can be an answer for 'work out' (thesaurus). I'm not certain of the remainder of the definition.
'very into that' is the wordplay.
'very' becomes 'v' (abbreviation).
'into' is an insertion indicator.
'that' becomes 'sole' (I am not sure about this - if you are sure you should believe this answer much more).
'v' put into 'sole' is 'SOLVE'.
(Other definitions for solve that I've seen before include "Settle" , "Get the answers" , "Unravel (a clue)" , "Figure out the answer" , "Find the key - work out" .)