Account of investigation, perhaps, is concerning Left (6)
I believe the answer is:
report
'account of investigation' is the definition.
'report' can be an answer for 'investigation'. I am not sure about the 'account of' bit.
'is concerning left' is the wordplay.
'is concerning' becomes 're' (both can mean on a particular topic).
'left' becomes 'port' (left side of a ship - opposite of starboard).
're'+'port'='REPORT'
'perhaps' is the link.
Can you help me to learn more?
(Other definitions for report that I've seen before include "Statement of facts, news etc - noise" , "Describe with a bang" , "Sharp sound of a gun firing" , "shop" , "Formal account of a matter" .)