Third person's conservative account of what happened (7)
I believe the answer is:
history
'what happened' is the definition.
(I've seen this in another clue)
'third person's conservative account' is the wordplay.
'third person's conservative' becomes 'hi' (I can't explain this - if you can you should give a lot more credence to this answer).
'account' becomes 'story' (story is a kind of account).
'hi'+'story'='HISTORY'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for history that I've seen before include "The record of past events" , "Old record" , "Background" , "Account of past events" , "eventful past" .)