Veronica's source of methamphetamine? (9)
I believe the answer is:
speedwell
'veronica's' is the definition.
(speedwell can mean a veronica plant)
'source of methamphetamine?' is the wordplay.
I cannot quite see how this works, but
'source' could be 'well' (well is a kind of source) and 'well' is found in the answer.
'methamphetamine?' could be 'speed' (I've seen this in another clue) and 'speed' is present in the answer.
No letters remain.
This explanation may well be incorrect...
(Other definitions for speedwell that I've seen before include "Flowering plant" , "bloomer?" , "Small creeping herbaceous plant with blue or pink flowers" , "Small plant, veronica" , "Small blue flower of the genus veronica" .)