Capital I invested in settee (5)
I believe the answer is:
sofia
'capital' is the definition.
(capital of Bulgaria)
'i invested in settee' is the wordplay.
'invested in' means one lot of letters goes inside another.
'settee' becomes 'sofa' (I've seen this before).
'i' put within 'sofa' is 'SOFIA'.
(Other definitions for sofia that I've seen before include "capital city" , "Capital of Bulgaria" , "capital place" , "Foreign city" , "European city" .)