Harris's Uncle appears in adventure musical (5)
I believe the answer is:
remus
'harris's uncle' is the definition.
(Uncle Remus, Joel Chandler Harris character)
'in adventure musical' is the wordplay.
'in' says the answer is hidden in the clue.
'REMUS' can be found hidden inside 'adventure musical'.
'appears' acts as a link.
(Other definitions for remus that I've seen before include "partner in City foundation" , "Brother of 15" , "One responsible for capital" , "Brother of Romulus" , "Co-founder of Rome" .)