Turned out duo slept through closing music (8)
I believe the answer is:
postlude
'closing music' is the definition.
The definition suggests a singular noun which matches the answer.
'turned out duo slept' is the wordplay.
'turned out' is an anagram indicator (turn out can mean to organise).
'duo'+'slept'='duoslept'
'duoslept' with letters rearranged gives 'POSTLUDE'.
'through' is the link.
Can you help me to learn more?
(Other definitions for postlude that I've seen before include "Afterword" , "epilogue" , "Concluding music piece" , "Used plot (anag) - final piece" , "Work" .)