Perplexing; mysterious (9)
I believe the answer is:
enigmatic
I believe this clue is a double definition.
'perplexing' is the first definition.
(I've seen this in another clue)
'mysterious' is the second definition.
(I've seen this before)
(Other definitions for enigmatic that I've seen before include "Obscure, puzzling" , "Ambiguous or puzzling" , "Puzzling, like the Sphinx" , "Like a puzzle" , "Mysterious or puzzling, like Mona Lisa's smile" .)