Most unusual, smuggling dope in threatened area (10)
I believe the answer is:
rainforest
'threatened area' is the definition.
(area threatened by deforestation)
'most unusual smuggling dope' is the wordplay.
'most unusual' becomes 'rarest' (I've seen this before).
'smuggling' means one lot of letters goes inside another (I've seen this in other clues).
'dope' becomes 'info' (I've seen this before).
'rarest' placed around 'info' is 'RAINFOREST'.
'in' acts as a link.
(Other definitions for rainforest that I've seen before include "Luxuriant tropical woodland" , "Dense luxuriant tropical zone" , "high-growth area" , "Tropical jungle" , "has lots of tropical trees" .)