Appeal to provide the head of police with a clue (5)
I believe the answer is:
plead
'appeal to' is the definition.
(thesaurus)
'the head of police with a clue' is the wordplay.
'the head of' says to take the initial letters.
'with' means one lot of letters go next to another.
'a clue' becomes 'lead' (I've seen this before).
The first letter of 'police' is 'p'.
'p'+'lead'='PLEAD'
'provide' acts as a link.
(Other definitions for plead that I've seen before include "Argue (a position in court)" , "Supplicate" , "State whether one is guilty or not" , "Appeal humbly (to)" , "Present an argument in court" .)