Most interesting bit about capital city? Vote (6)
I believe the answer is:
climax
'most interesting bit' is the definition.
(most interesting part of a story)
'about capital city? vote' is the wordplay.
'about' becomes 'c' (abbreviation for circa).
'capital city?' becomes 'Lima' (capital of Peru).
'vote' becomes 'x' (how votes are marked).
'c'+'lima'+'x'='CLIMAX'
(Other definitions for climax that I've seen before include "Most exciting point" , "(Reach the) highest level" , "Crux, turning point" , "Peak of a performance" , "Most intense point" .)