Hopefully one name will lead to arrest over heroin (9)

'hopefully one' is the definition.
I know nothing about this answer so I can't judge whether this works.

'name will lead to arrest over heroin' is the wordplay.
'name' becomes 'n' (common abbreviation e.g. on forms).
'will' becomes 'ishall' (I can't justify this - if you can you should believe this answer much more).
'lead to' indicates taking the first letters.
'over' indicates putting letters inside.
'heroin' becomes 'H' (H is a slang term for heroin).
The first letter of 'arrest' is 'a'.
'ishall'+'a'='ishalla'
'n' placed into 'ishalla' is 'inshalla'.
'inshalla'+'h'='INSHALLAH'

Can you help me to learn more?