Novel isn't about that Spanish investigation (7)
I believe the answer is:
inquest
'investigation' is the definition.
(I know that inquest is a type of enquiry)
'novel isn't about that spanish' is the wordplay.
'novel' indicates anagramming the letters (letters in a new or novel order).
'about' is an insertion indicator.
'that spanish' becomes 'que' ('that' in Spanish).
'isnt' is an anagram of 'inst'.
'inst' enclosing 'que' is 'INQUEST'.
(Other definitions for inquest that I've seen before include "Judicial inquiry" , "Post-mortem investigation" , "Investigation by coroner" , "What-went-wrong investigation" , "Post-death enquiry" .)