Maze-running rodent (3)
I believe the answer is:
rat
'maze-running rodent' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for rat that I've seen before include "Treacherous person" , "Plague-carrying rodent" , "Contemptible person" , "Strike-breaker" , "one who deserts the sinking ship?" .)