Detectives number sample (3,2)
I believe the answer is:
dip in
'sample' is the definition.
(I've seen this before)
'detectives number' is the wordplay.
I cannot really understand how this works, but
'number' could be 'pin' (I've seen this before) and 'pin' is present in the answer.
The remaining letters 'di' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for dip in that I've seen before include "Take a share" , "Sample" .)