Marsh transformed in Goa? (5)
I believe the answer is:
ngaio
'marsh' is the definition.
(crime writer Ngaio Marsh)
'transformed in goa?' is the wordplay.
'transformed' is an anagram indicator.
'in'+'goa'='ingoa'
'ingoa' anagrammed gives 'NGAIO'.
(Other definitions for ngaio that I've seen before include "- Marsh, NZ detective novelist" , "wood" , "foreign tree" , "- - Marsh, crime writer" , "New Zealand tree" .)