It sure would seem so when my novel comes out.
I had an agent once who told his clients that, "Ideas float on the wind. Several people might pick up the same idea at the same time. That's not to mean one author is stealing from another or plagiarizing another's plot."
With this in mind, I watched in horror as part of the plot for my new Occult novel 'floated' across my TV screen. The weekly show I was watching is called 'Criminal Minds', one of my favorites. This past week the plot was similar to mine with a few exceptions. The characters were different, the main villain was different, but everything else was the same.
I don't know if this fear hits you when this takes place--everyone will swear I stole the plot and changed it to seem a bit different. This isn't true and it happens all of the time: in books, movies, TV programs and stage plays. However, here's the downer: Critics are quick to point out the similarites in your work to the already released work of another author. One NY critic even uses a side-by-side column to show the similarites in your work and others. Then his column ends with a question mark, leaving it up to the reader to decide if an author plagiarized a plot.
Something like this can end an author's career if readers believe you cheat. It especially happens when the name of your work is also similar to the already released work. I know you cannot copyright a name, but it looks suspicious when names are very similar.
When my first mystery, 'Unholy Alliance' was published, I knew it was being sold on Amazon, so I went there and did a search. I almost fainted when I discovered that over a dozen other novels were either named the same or had the expression, 'Unholy Alliance' in their titles. I cringed. But hey, it happens. However, even knowing this, I don't get any less disturbed.
My point is: Don't let it stop you from finishing your work. I won't, why should you? Stuff happens. As an author you'll discover the same thing happening over and over as you write. Just keep going because so long as the plots aren't exactly the same as what's already been released, you're safe.
A friend of mine once bought a novel on sale at a library. After reading the novel, she was alarmed because the plot was the same as my plot in 'Deathbringer', a horror novel published by Dorchester. Although the publishers were different, the plot wasn't. Certain scenes from my novel had been copied verbatim. I considered suing the authors--two brothers. But since their novel went nowhere, it would've cost me more to sue than I'd recoup. If someone does this to you, make sure it's a bestseller or you're just knocking your head against a wall.
That's the danger of someone outright plagiarizing your work.