High capital growth ultimately when investing in the City (5)
I believe the answer is:
lhasa
'high capital' is the definition.
(capital of Tibet)
'growth ultimately when investing in the city' is the wordplay.
'ultimately' indicates one should take the final letters.
'when' becomes 'as' (eg 'when I walked' means 'as I walked').
'investing in' means one lot of letters goes inside another.
'the city' becomes 'LA' (Los Angeles).
The final letter of 'growth' is 'h'.
'h'+'as'='has'
'has' inserted inside 'la' is 'LHASA'.
(Other definitions for lhasa that I've seen before include "Asian capital" , "Sacred city" , "Tibet's "Forbidden City"" , "foreign capital" , "The Forbidden City in Tibet" .)