Capital adequately invested in toy making (5)
I believe the answer is:
tokyo
'capital' is the definition.
(capital of Japan)
'adequately invested in toy making' is the wordplay.
'adequately invested' becomes 'ok' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'in' indicates putting letters inside.
'making' indicates an anagram.
'toy' is an anagram of 'tyo'.
'ok' put within 'tyo' is 'TOKYO'.
Can you help me to learn more?
(Other definitions for tokyo that I've seen before include "eastern city" , "Capital of Japan" , "City once called Edo" , "Asian capital" , "Large Japanese city" .)