Sensible group of investigators has uncovered clue first (5)
I believe the answer is:
lucid
'sensible' is the definition.
(I've seen this before)
'group of investigators has uncovered clue first' is the wordplay.
'group of investigators has' becomes 'cid' (I am not sure about this - if you are sure you should believe this answer much more).
'uncovered' says to take the centre.
'first' says to put letters next to each other.
The centre of 'clue' is 'lu'.
'cid' after 'lu' is 'LUCID'.
Can you help me to learn more?
(Other definitions for lucid that I've seen before include "Shining, clearly" , "between raves?" , "Compos mentis" , "Clear, intelligible" , "Clear, easy to understand" .)