What does the cryptic crossword clue "Imagines content being rewritten to create a mystery (6)" mean?

The definition is "a mystery". The wordplay uses an anagram. anagram of MAGINE = ENIGMA; definition: "a mystery" The answer is ENIGMA.

Imagines content being rewritten to create a mystery (6)

Guardian Cryptic #29119 | 3 Down | 2023-07-11 flower