Work in the theatre (9)
'work' is the definition.
(operation is a kind of work)
'theatre' is the wordplay.
I cannot quite see how this works, but
'theatre' could be 'opera' (opera is a kind of theatre) and 'opera' is located in the answer.
This explanation may well be incorrect...
'in the' acts as a link.
Can you help me to learn more?
(Other definitions for operation that I've seen before include "financial transaction" , "Handling" , "running" , "activity" , "Surgical or military piece of work" .)
(Other definitions for operate that I've seen before include "effect" , "(Of machine) function" , "Act in a theatre" , "Control, run, a machine say" , "Work, function" .)