On the contrary, agent securing final group of actors could be just what the doctor ordered (7,4)
I believe the answer is:
plaster cast
'be just what the doctor ordered' is the definition.
I can't tell whether this definition defines the answer.
'on the contrary agent securing final group of actors' is the wordplay.
'on the contrary' shows that the letters should be reversed in order (letters in the opposite or contrary direction).
'agent' becomes 'rep' (short for representative).
'securing' is an insertion indicator.
'final' becomes 'last' (synonyms).
'group of actors' becomes 'cast' (group of actors in a production).
'rep' backwards is 'per'.
'per' enclosing 'last' is 'plaster'.
'plaster'+'cast'='PLASTER CAST'
'could' is the link.
Can you help me to learn more?
(Other definitions for plaster cast that I've seen before include "Copy made by pouring mixture into a mould - art class pet (anag)" , "Copy of an object made in a mould" , "Protection for broken limbs etc" , "sign of a break" , "Aid to bone-setting" .)