Turn unknown informant in empty garage (6)
I believe the answer is:
gyrate
'turn' is the definition.
(gyrating is a kind of turning)
'unknown informant in empty garage' is the wordplay.
'unknown' becomes 'y' (algebra).
'informant' becomes 'rat' (rat is a kind of informant).
'in' indicates putting letters inside.
'empty' says to hollow out the word (remove centre letters).
'garage' with its middle taken out is 'ge'.
'y'+'rat'='yrat'
'yrat' placed into 'ge' is 'GYRATE'.
(Other definitions for gyrate that I've seen before include "Move rapidly in a circle" , "Revolve, whirl" , "Twirl" , "Move with a circular motion" , "Move in a spiral course" .)