A lot must, surprisingly revealing all? (3,5)
I believe the answer is:
sum total
'all?' is the definition.
(thesaurus)
'a lot must surprisingly' is the wordplay.
'surprisingly' indicates an anagram.
'a'+'lot'+'must'='alotmust'
'alotmust' is an anagram of 'SUM TOTAL'.
'revealing' is the link.
(Other definitions for sum total that I've seen before include "The lot" , "Result of addition" , "The final aggregate" , "Final addition" .)