Capital remains very poorly invested in Nationwide's banks (9)
I believe the answer is:
nashville
'capital' is the definition.
(state capital of Tennessee)
'remains very poorly invested in nationwide's banks' is the wordplay.
'remains' becomes 'ash' (remains of a fire).
'very' becomes 'v' (abbreviation).
'poorly' becomes 'ill' (synonyms).
'invested in' means one lot of letters goes inside another.
'banks' means to remove the middle letters (the banks are the edges of the word).
'nationwide' with its middle removed is 'ne'.
'ash'+'v'+'ill'='ashvill'
'ashvill' placed inside 'ne' is 'NASHVILLE'.
(Other definitions for nashville that I've seen before include "US city" , "Centre of country and western" , "Tennessee state capital" , "Grand Ole Opry city" , "Where the Grand Ole Opry comes from" .)