What does the cryptic crossword clue "Sort loth to engage with characters in book? (9)" mean?

The definition is "Sort loth to engage with characters in book?". The wordplay uses a cryptic definition. Cryptic definition The answer is NONREADER.

Sort loth to engage with characters in book? (9)

Times Cryptic #28721 | 16 Across | 2023-09-29 flower