Characters
I once asked this literary agent what writing paid the best, and he said, "ransom notes."
— Harry Zimm · Get Shorty

Behind the line May contain spoilers.
Our reading
An editorial interpretation.
The speaker tells a wry story about asking a literary agent which kind of writing earns the most, and the agent answering with ransom notes. The gag is cynical: real money supposedly lies in menacing demands, not in books, poems or respectable literature.
Context reviewed