Complicated to work out (9)
I believe the answer is:
elaborate
I believe this clue is a double definition.
'complicated' is the first definition.
(I've seen this before)
'work out' is the second definition.
(I know that work out can be written as elaborate)
'to' acts as a link.
(Other definitions for elaborate that I've seen before include "Complicated - work out" , "Fussy" , "Add details to clarify meaning" , "Ostentatious, possibly" , "Describe in detail, being complicated" .)