"The Maltese Falcon" sleuth (5)
I believe the answer is:
spade
'the maltese falcon sleuth' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for spade that I've seen before include "that has a cutting edge" , "Fictional detective" , "one of thirteen?" , "Digger" , "Digging tool" .)