manic mary...
35d change jacobi's "core" CO to LE (the in French)
18d nice refers to Nice in France ... hence French old length.. Persic is extra.... couple of articles here and there means you need an English article "a" + a French one "une" . Together they make the length required.
You should have an author at 20a .....replace with one of his best known works(it was a film too) (1,5,7)
Then you need an actual figure in front of this for the whole title... so change the clue number 21 to 01
6d needs to be changed to the antagonist of the book ... i think it's already been mentioned in the thread .. it's 3 letters with 4 numbers after it