The subject of plagiarism came up recently in the bookshop.
According to American comic-book writer Peter David, one is often inspired by another writer's work.
"One can take a concept or an idea... and twist it around and transpose it and make it into your own. This takes work.
"It is also possible to take the aforementioned concept or idea or bit of business and put it in its entirety in your story. It's possible to do this unintentionally. This is called "happenstance."
And if you realize it while there's still time to do something about it, then either you excise it or else acknowledge the source. This is called "honesty."
"However, if you do it deliberately, hoping to pull a fast one, that's called "plagiarism," from the Latin root meaning "kidnapper." To put it mildly, it's frowned upon. To put it unmildly, it's actionable in a court of law."

Peter David, But I Digress, krause publications, 1994.