Torquemada's last puzzle — wow! (5)
I believe the answer is:
amaze
'wow' is the definition.
(I've seen this in another clue)
'torquemada's last puzzle' is the wordplay.
'last' suggests the final letters.
'puzzle' becomes 'maze' (maze can mean a puzzling situation).
The last letter of 'torquemada' is 'a'.
'a'+'maze'='AMAZE'
(Other definitions for amaze that I've seen before include "Stagger" , "Greatly surprise, astound" , "Startle" , "Confound with wonder" , "Floor" .)