Detectives getting queen a drink (5)
I believe the answer is:
cider
'a drink' is the definition.
(I know that cider is a type of drink)
'detectives getting queen' is the wordplay.
'detectives' becomes 'CID' (abbreviation for Criminal Investigation Department).
'getting' means one lot of letters go next to another.
'queen' becomes 'ER' (abbreviation for Elizabeth Regina).
'cid'+'er'='CIDER'
(Other definitions for cider that I've seen before include "Apple-based beverage" , "Alcohol from apples" , "Alcoholic drink (to be taken with Rosie?)" , "Alcoholic drink from fermented apple juice" , "Drink made from pears" .)