The most common and most likely answer to this crossword clue is the 8 letter word CLARISSA
I've seen this crossword clue in The Guardian
C
L
A
R
I
S
S
A
More clues leading to the result CLARISSA
Buddy explains!
The straight part
We know that "Subject of 13 novel" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case subject of 13 novel = clarissa.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.