Quietly request saint be replaced by a novice in the backstory (7)
I believe the answer is:
prequel
If this is the answer I cannot explain how the clue works.
Can you help me to learn more?
(Other definitions for prequel that I've seen before include "Story preceding another" , "Possibly book in advance" , "What happened before" , "A story beginning prior to the start of the original one" , "Young Sherlock Holmes, say" .)