Guarded by that expert sleuth Edward (9)
I believe the answer is:
protected
'guarded' is the definition.
(thesaurus)
'by that expert sleuth edward' is the wordplay.
'by' means one lot of letters go next to another.
'that expert' becomes 'pro' (I've seen this before).
'sleuth' becomes 'tec' (short for detective).
'edward' becomes 'ted'.
'pro' put next to 'tec' is 'protec'.
'protec'+'ted'='PROTECTED'
(Other definitions for protected that I've seen before include "Safeguarded, shielded from danger" , "Sheltered" , "Kept from harm" .)