What you need to write a story for the theatre (6)
I believe the answer is:
talent
'what you need to' is the definition.
I can't judge whether this defines the answer.
'a story for the theatre' is the wordplay.
'a story' becomes 'tale' ('tale' can be a synonym of 'story').
'for' says to put letters next to each other.
'the theatre' becomes 'NT' (National Theatre).
'tale'+'nt'='TALENT'
'write' is the link.
Can you help me to learn more?
(Other definitions for talent that I've seen before include "Genius" , "ancient currency" , "Special ability of some kind" , "Skill, natural ability" , "some scouts are looking for" .)