Help check text of plot within trial (7)
I believe the answer is:
subedit
'help check text' is the definition.
(subeditors check text for errors)
'plot within trial' is the wordplay.
'plot' becomes 'bed' (bed is a kind of plot).
'within' indicates putting letters inside.
'trial' becomes 'suit' (as in a legal suit).
'bed' put within 'suit' is 'SUBEDIT'.
'of' is the link.
(Other definitions for subedit that I've seen before include "Check newspaper copy" , "Copyread" , "Prepare for publishing" , "to work on newspaper" , "Headline writer does" .)