Child investigator held by Tory fringe for betrayal (9)
I believe the answer is:
treachery
'for betrayal' is the definition.
(synonyms)
'child investigator held by tory fringe' is the wordplay.
'child investigator' becomes 'reacher' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'held by' is an insertion indicator.
'fringe' says to hollow out the word (remove centre letters) (only the letters on the fringe).
'tory' with its centre removed is 'ty'.
'reacher' going into 'ty' is 'TREACHERY'.
Can you help me to learn more?
(Other definitions for treachery that I've seen before include "Perfidious behaviour" , "Two-timing" , "Deceptiveness" , "Double-dealing" , "disloyalty" .)