What does the cryptic crossword clue "Book horrifying production company, extremes trimmed back (4)" mean?

The definition is "Book". The wordplay uses a reversal. AMME (reversal="AMME") = EMMA; definition: "Book" The answer is EMMA.

Book horrifying production company, extremes trimmed back (4)

Guardian Cryptic #29304 | 26 Across | 2024-02-13 flower