Composer wandering in alien parts (10)
I believe the answer is:
palestrina
'composer' is the definition.
(Giovanni Pierluigi da Palestrina)
'wandering in alien parts' is the wordplay.
'wandering in' indicates anagramming the letters (I've seen this in other clues).
'alien'+'parts'='alienparts'
'alienparts' is an anagram of 'PALESTRINA'.
(Other definitions for palestrina that I've seen before include "musician" , "He composed music" , "16th century Italian choral composer" , "Italian Renaissance composer" .)