How many letters does the top answer for “wrote mortal engines quartet” have?

The most common answer is reeve (5 letters).

Crossword clue: wrote mortal engines quartet

1 answer found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

reeve 5 letters wd-fact-v3

female ruff

author of mortal engines quartet 60% similar → reeve