Captivated by a fiend's cat? Weird! (10)
I believe the answer is:
fascinated
'captivated' is the definition.
('fascinate' can be a synonym of 'captivate')
'a fiend's cat? weird' is the wordplay.
'weird' is an anagram indicator.
'a'+'fiends'+'cat'='afiendscat'
'afiendscat' with letters rearranged gives 'FASCINATED'.
'by' acts as a link.
(Other definitions for fascinated that I've seen before include "Irresistably attracted" , "Irresistibly interested" , "Captivated" , "Bewitched, enthralled" , "captured" .)