A pope's man metamorphosed in a novel (9)
I believe the answer is:
gregorian
'a pope's man metamorphosed in a novel' is the definition.
I can't tell whether this definition defines the answer.
'man metamorphosed in a novel' is the wordplay.
'man metamorphosed' becomes 'Gregor' (Gregor Samsa from Franz Kafka's The Metamorphosis).
'novel' indicates an anagram (letters in a new or novel order).
'in'+'a'='ina'
'ina' anagrammed gives 'ian'.
'gregor'+'ian'='GREGORIAN'
(Other definitions for gregorian that I've seen before include "Like sixteen popes" , "monk's singing" , "Sort of chant" , "Type of calendar, of chant" , "relating to calendar" .)