Have discussions about a key overseas office (9)
I believe the answer is:
consulate
'overseas office' is the definition.
(office of another country's consul)
'have discussions about a key' is the wordplay.
'have discussions' becomes 'consult' (have consultations).
'about' indicates putting letters inside.
'key' becomes 'e' (musical key).
'consult' placed around 'a' is 'consulat'.
'consulat'+'e'='CONSULATE'
(Other definitions for consulate that I've seen before include "Diplomatic mission" , "embassy" , "office" , "Diplomatic residence" , "Government official in a foreign country" .)