I understand that I can't write "The Diaries of Severus Snape" without a lot of lawyers coming after me brandishing sticks and cease-and-desist notices. But I can write about a wizard in a boarding school.
But let's have a look at this one:
Back in 2017, the winner of the "Festival of German-Language Literature" - was a short story (3000 words) with the following premise:
The driver of a frozen food truck is asked by one of his clients to help him get rid of a body - his own. The client will commit suicide by placing himself in his freezer, and the driver is asked to ditch the body where it won't be found (easily). But when the driver shows up at the next delivery day, the freezer is empty and the client can't be found...
This is where the short story ended in 2017; this year, the author has published a full novel spinning the story further (apparently the driver goes in search of the client).
I have no intention of reading the novel (I didn't like the execution of the short story, let's say it was too literary for my taste) but I do find the premise intriguing enough to build my own writing upon it.
The question is now: can I do this? Or is this specific idea one that is so far out there, so unique that the author has a kind of monopoly on it? Or in other words: Where is the line when you start copying / plagiarizing an idea?
You can't plagiarize an idea.
Or a concept.
Copyright is mercurial for sure, but the one standard is: copyright applies to actual words on the page. Or electrons on your screen.
Ideas are fair game.
But that's not the question you want to ask.
Plagiarism isn't the problem.
Being derivative is the problem.
What do I mean by derivative?
You don't want to write something that so closely evokes another work that I think "been there, read that."
Agents are looking for things that are fresh and new.
(Almost) every crime novel has a victim, a killer and a cop. What fresh spin you put on those stock characters is how you write something fresh and new.
So, can your detective wear Hawaiian shirts and carry a Dan Wesson .38 like Elvis Cole?
Sure, but you should know that if you do that, I've read every Elvis Cole novel and I'll recognize that description instantly.
Can your detective shoot a smiley face into the target at the gun range?
Sure, but I'm going to think Mel Gibson and Lethal Weapon.
Can your detective be a sharp eyed clever spinster who lives in St. Mary Mead?
Sure, but I've already met Miss Marple.
The trick is to either acknowledge the inspiration:
"I carried a Dan Wesson .38 cause Elvis Cole did"
"You shot out a smiley face. Who do you think you are? Martin Riggs?"
Betty Buttonweezer loved Agatha Christie novels, she just hadn't planned on becoming Miss Marple, but here she was in St. Mary Mead, knitting.
or give it some sort of twist so I recognize the reference but it's got a fresh spin.
Romeo and Juliet on the Upper West Side-fresh twist.
Beowulf by Maria Dahvana Headley--really fresh twist
Miss Marple is the killer---oh, geeze, someone get on that please.
Plagiarism is stealing words.
Inspiration is looking at someone else's work and being moved to create your own.