Criminal gang sending missile back over island (5)
I believe the answer is:
triad
'criminal gang' is the definition.
(I've seen this before)
'missile back over island' is the wordplay.
'missile' becomes 'dart' (dart is a small missile).
'back' says the letters should be written backwards.
'over' indicates putting letters inside.
'island' becomes 'i' (geographical abbreviation).
'dart' written backwards gives 'trad'.
'trad' going around 'i' is 'TRIAD'.
'sending' acts as a link.
This may not be correct. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for triad that I've seen before include "Chinese criminal society" , "Could be major" , "three making a sound?" , "Union of three" , "trio" .)