Betrays count — and his successor? (5,2)
I believe the answer is:
tells on
'betrays' is the definition.
('tell on' can be a synonym of 'betray')
'count and his successor?' is the wordplay.
'count' becomes 'tell' (I've seen this before).
'and' is a charade indicator (letters next to each other).
'his successor?' becomes 'son' (I am not sure about this - if you are sure you should believe this answer much more).
'tell'+'son'='TELLS ON'
(Other definitions for tells on that I've seen before include "Reports bad behaviour" , "shops" .)