Go astray in the middle of Derry (3)
I believe the answer is:
err
'go astray' is the definition.
(to err is to make an error or go the wrong way)
'middle of derry' is the wordplay.
'middle of' says the answer is hidden in the clue (the answer is somewhere in the middle of the clue).
'ERR' is hidden in the letters of 'derry'.
'in the' is the link.
(Other definitions for err that I've seen before include "Go astray" , "Make mistake in Canberra" , "Go wrong" , "Blunder" , "Bungle" .)