there will be a fish

IT ACTUALLY IS, YES. It's essentially a tie-in novel, but they wrote it as if it was actually the book Castle's been writing; the "author" is "Richard Castle," and the acknowledgments section was done in-character. There are lots of inside jokes to the series (like, things that Castle has said "ooh, I should write that into the book," and then he apparently did, and the sex scene actually is on page 105! <3), but it stands on its own as a fun pulp mystery novel. I recommend it! I bought an e-book copy and quite enjoyed the read.