Fish in a corner (5)
I believe the answer is:
angle
I believe this clue is a double definition.
'fish' is the first definition.
(angle can mean to fish)
'corner' is the second definition.
(eg a corner of a shape)
'in a' is the link.
(Other definitions for angle that I've seen before include "fork" , "Heat (metal) and allow to cool to remove stresses" , "Germanic invader" , "Approach to problem" , "may be right" .)