Plant unknown agent in front (7)
I believe the answer is:
factory
'plant' is the definition.
(I know that factory is a type of plant)
'unknown agent in front' is the wordplay.
'unknown' becomes 'y' (algebra).
'agent' becomes 'factor' (business term for a representative).
'in front' says to put letters next to each other.
'y' put after 'factor' is 'FACTORY'.
(Other definitions for factory that I've seen before include "mill" , "Works" , "Things are made here" , "Place for production" , "Manufacturing plant" .)