Investigators meeting queen for drink (5)
I believe the answer is:
cider
'for drink' is the definition.
(cider is a kind of drink)
'investigators meeting queen' is the wordplay.
'investigators' becomes 'CID' (Criminal Investigation Department).
'meeting' is a charade indicator (letters next to each other).
'queen' becomes 'ER' (abbreviation for Elizabeth Regina).
'cid'+'er'='CIDER'
(Other definitions for cider that I've seen before include "Alcoholic drink made from apples" , "Apple-based drink" , "Drink made from pears" , "Alcohol from apples" , "Alcoholic drink (to be taken with Rosie?)" .)