Unite about taking on doctor's scheme (8)
I believe the answer is:
intrigue
'scheme' is the definition.
(synonyms)
'unite about taking on doctor's' is the wordplay.
'about' indicates anagramming the letters.
'taking on' means one lot of letters goes inside another.
'doctor' becomes 'rig' (I've seen this before).
'unite' with letters rearranged gives 'intue'.
'intue' placed around 'rig' is 'INTRIGUE'.
(Other definitions for intrigue that I've seen before include "A conspiracy or an affair" , "Secret love affair" , "pique?" , "Secret plot or affair" , "Arouse the curiosity of" .)