Quite unemotional senior detective about to arrest Green and Liberal (3-4)
I believe the answer is:
ice-cold
'quite unemotional' is the definition.
(ice-cold can mean cool or unemotional)
'senior detective about to arrest green and liberal' is the wordplay.
I cannot quite see how this works, but
'senior' could be 'old' (associated in meaning) and 'old' is found in the answer.
'about' could be 'c' (circa) and 'c' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
(Other definitions for ice-cold that I've seen before include "Chilled" , "Straight from the freezer" , "Frozen" , ". . . . . . . in Alex (film)" , "Freezing" .)