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' can be found hidden inside '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" .)