25 across
As
part
of
detective
force,
sent
first
off
to
disturbance
(8)
As part of detective force, sent first off to disturbance (8)
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The definition is at the end of the clue.
How the clue works
Look at disturbance at the end — that's what you're defining. You build the answer with as part of giving you IN, then detective force giving you CID (the Criminal Investigation Department), and finally sent first off means you lop the first letter off SENT to get ENT.