Suspect foul play (5,1,3)
I believe the answer is:
smell a rat
'suspect foul play' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for smell a rat that I've seen before include "Become suspicious" , "Sense something is amiss" , "Sense something suspicious" , "Have suspicion something is afoot" , "Suspect something's amiss" .)