Bedtime books about shape-shifting ghost universal (6,3)
I believe the answer is:
lights out
'bedtime' is the definition.
(lights out is a kind of bedtime)
'about shape-shifting ghost universal' is the wordplay.
'about' is an insertion indicator.
'shape' becomes 'lit' (I can't justify this - if you can you should believe this answer much more).
'shifting' indicates anagramming the letters.
'universal' becomes 'U' (film certificate).
'ghost'+'u'='ghostu'
'ghostu' anagrammed gives 'ghtsou'.
'lit' enclosing 'ghtsou' is 'LIGHTS-OUT'.
'books' is the link.
I am not very happy about this link. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for lights out that I've seen before include "when one should be ready to retire" , "call at night?" , "when it's time to retire" , "Bedtime signal" , "Departs" .)