Spy, note, probing a lot of evidence of murder? (4)
I believe the answer is:
bond
'spy' is the definition.
(James Bond)
'note probing a lot of evidence of murder?' is the wordplay.
'note' becomes 'n' (abbreviation).
'probing' is an insertion indicator (probe can mean to poke or prod into).
'a lot of evidence of murder?' becomes 'bod' (I am not sure about this - if you are sure you should believe this answer much more).
'n' inserted within 'bod' is 'BOND'.
Can you help me to learn more?
(Other definitions for bond that I've seen before include "Binding agreement; double zero seven" , "Tie - debenture" , "Fastening; financial certificate" , "secure?" , "one licensed to kill" .)