Son harbours desire to be a theatre worker? (7)
I believe the answer is:
surgeon
'a theatre worker?' is the definition.
(I've seen this before)
'son harbours desire' is the wordplay.
'harbours' indicates putting letters inside.
'desire' becomes 'urge' (I've seen this before).
'son' enclosing 'urge' is 'SURGEON'.
'to be' acts as a link.
(Other definitions for surgeon that I've seen before include "Naval doctor" , "Theatre operator" , "Medical practitioner - go nurse (anag)" , "Operating medical practitioner" , "9 practitioner (through keyhole?)" .)