Night before book incident (5)
I believe the answer is:
event
'incident' is the definition.
(an incident is an event or happening)
'night before book' is the wordplay.
'night before' becomes 'eve' (eve can mean the night before something).
'book' becomes 'NT' (New Testament).
'eve'+'nt'='EVENT'
(Other definitions for event that I've seen before include "Affair" , "Happening, noteworthy perhaps" , "pole vault maybe" , "Something going on" , "Planned public or social occasion" .)