Plant detective, getting smart (9)
I believe the answer is:
eyebright
'plant' is the definition.
'detective getting smart' is the wordplay.
'detective' becomes 'eye' (I've seen this in other clues).
'getting' says to put letters next to each other.
'smart' becomes 'bright' (synonyms).
'eye'+'bright'='EYEBRIGHT'
(Other definitions for eyebright that I've seen before include "that could help the viewer" , "Wild flower - get by hire (anag)" , "White-flowered plant" , "Small plant" , "Traditional remedy for vision problems" .)