Investigation by partner when the game is finished (9)
I believe the answer is:
checkmate
'game is finished' is the definition.
I can't judge whether this definition defines the answer.
'investigation by partner when' is the wordplay.
'investigation' becomes 'check' (check is a kind of investigation).
'by' means one lot of letters go next to another.
'partner when' becomes 'mate' (synonyms. I am not sure about the 'when' bit.).
'check'+'mate'='CHECKMATE'
'the' acts as a link.
Can you help me to learn more?
(Other definitions for checkmate that I've seen before include "Chess game ending" , "final defeat" , "Declaration of chess victory" , "The final winning move in chess" , "Winning call on board" .)