Police unit will be involved in action for certain (7)
I believe the answer is:
decided
'certain' is the definition.
(I've seen this in another clue)
'police unit will be involved in action' is the wordplay.
I cannot quite understand how this works, but
'police' could be 'cid' (abbreviation for Criminal Investigation Department) and 'cid' is found within the answer.
'action' could be 'deed' (deed is a kind of action) and 'deed' is present in the remaining letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
'for' acts as a link.
Can you help me to learn more?
(Other definitions for decided that I've seen before include "Determined; resolute" , "Definite; agreed" , "Resolute; settled" , "Made up one's mind" , "Came to a resolution" .)