Suspect trickery (5,1,3)
I believe the answer is:
smell a rat
'suspect trickery' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for smell a rat that I've seen before include "Suspect deception" , "Detect something suspicious" , "Suspect something's amiss" , "Find something fishy" , "Sense something suspicious" .)