What does the cryptic crossword clue "Part of a bigger story provided by Mantel isn't bad (10)" mean?

The definition is "Mantel isn’t". The wordplay uses an anagram. anagram of MANTEL + ISN'T = INSTALMENT; definition: "Part" The answer is INSTALMENT.

Part of a bigger story provided by Mantel isn't bad (10)

Times Cryptic #28687 | 28 Across | 2023-08-21 flower