What does the cryptic crossword clue "Writer's book contains clever mixed metaphors (3,6)" mean?

The definition is "Writer". The wordplay uses an anagram. anagram of METAPHORS = TOMSHARPE; definition: "Writer's" The answer is TOMSHARPE.

Writer's book contains clever mixed metaphors (3,6)

Guardian Cryptic #28638 | 29 Across | 2021-12-27 flower