Idiot whose whereabouts are a puzzle? (5)
I believe the answer is:
wally
This clue is a double definition.
'idiot' is the first definition.
(wally can mean a stupid person)
'whose whereabouts are a puzzle?' is the second definition.
(as in Where's Wally puzzle books)
(Other definitions for wally that I've seen before include "Complete idiot" , "Idiot (slang)" , "A fool (sl.)" .)