The plot is good and interesting, though some grammar mistakes are found. All you need is a little practice. Since my native language is not English just like yours, I can suggest to you what I am doing to improve in the grammar part based on the reviews of my story.
Read the story now
1. Learn punctuation in the compound and complex sentences. Remember the Grammarly app pointing this always. I think it's better to learn it rather than trusting an app.
2. Learn passive and active voice rules, as we tend to mix these a lot.
3. Improve vocabulary. I bought a few classics in English literature recently to know the different ways to tell a story and improve vocabulary.
It's okay not to be good at these, we can always fix them with little effort and patience. Trust me you have a really good plot, with these mistakes taken care of, it will be an all five-star story :)
All the best!