Same plot but different story, is it plagiarizing?

Question

I'm writing a novel and is planning to publish it but then, I found out that someone else has already written a novel similar to mine. Both of our novel has similar plot but different story and settings.

Plot of story: A noble girl save a man with no identities, therefore, gives him a name. They both solve mysterious cases together and fall in love. The male and female protagonist then later got married. Things happen and the male protagonist lost his memories of the female protagonist and left her. The female protagonist then finds out about the male protagonist real identity (a prince) and follows him to his kingdom. There is also time traveling in the story.

My Story: Involves supernatural, demons, vampires, ghost, mythical creatures, exorcism, curses, past lives, wars, gods, and deities.

Their Story: Gathering lost jewels. Each case involves a jewel piece.

Answer 1

It's all been done before:

I am not joking when I say I think I've answered this question before, but I can't seem to find the reference. The fact is, every possible story has been done before - at least twice. The ancients already had most of the plot lines in broad terms while still in the BC's. I suspect if the library of Alexandria hadn't burned, even Shakespeare wouldn't have been able to claim originality.

This doesn't mean you shouldn't write, or that it's okay to copy other people's works. The fact is that you came up with the story line on your own, and as long as you aren't seeking to copy someone else (consciously or unconsciously) you aren't plagiarizing. If you make a study of mythology (and there's a Mythology SE if you want to check it out) there are plenty of stories of princes/princesses who are cursed, and who can't remember or acknowledge their past, and/or are subsequently cursed/made to forget/tricked into abandoning their true loves. There is a Russian one very close to this (I can't remember the name).

The key is to make it your own. Sleeping beauty is a Lesbian and is saved by the princess. The vampire is romantically involved with a sentient octopus and is a deep sea diver. Romeo and Juliet are five years old and there's a happy ending. Whatever.

I was 90% through a novel when I discovered that there were similarities between it and the Oresteia, a series of Greek tragedies. The ancient Greeks aren't likely to challenge me in court, so I ran with it and tweaked my story to embrace the mythology. I was already using Artemis and Nemesis as characters. So if the similarities are because you both drew inspiration from a common mythology, then naturally the stories will have similarities.

While you can't and shouldn't change your story to be in line with contemporary stories, you could certainly tweak it to be LESS like those, if desired. Are there similarities that make it look like you are copying? Do they derive from a common literary source, or is it coincidence? Two very similar characters with very similar names (Alice vs Alecia, for example) might look suspicious. Unless there's a significant reason to keep a detail like that in (like you got it from Alice in Wonderland) then feel free to change it. Who knows, maybe THEY got it from Alice in Wonderland, and it IS a common story origin.