Hi everybody,
First, you have to know that english is not my mother tongue so....my english could be trashy.
So, i have to write the back cover of my own thriller...I have to imagine the title and my pen name...I have to write about a plot in three short paragraphs. The setting is my high school (called Stanisles) and I am free to imagine the story. I gotta use the simple present to create suspense and finish with suspension points... The aim is to make people feel like reading my book.
That's what I've done:

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A detention afternoon, in addition on a Saturday, because of a homework forgotten at home, Haley James, feeling antagonized and injustice, decide to follow Nathan Scott, his boyfriend and his clique who want to explore their high school Stanislas…

A stumble, a hatch which collapse, an arcane and never ending subterranean…the escapade turn into an adventure and the adventure turn out to be the worst nightmare ever when they found out three skeletons trapped behind a door closed from the outside. The worst is still to come since no one knows how to get out…

When Nathan releases a thirty years old secret, each one of his friends started to be mysteriously killed by something that appears to be the Grim Reaper…
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Could you please correct this? and why not improve it? (well, in fact i gotta add 30 extra words)
Thanks a lot, I really do appreciate it.
here is the last version of my work:
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DIABOLIC WALK
By Sy Marshal

On a Saturday afternoon, in detention, because of a homework forgotten at home, Haley James, feeling antagonized and injustice, decides to follow Nathan Scott, his boyfriend, and his clique who want to explore their high school_Stanislas…

A stumble, a hatch collapses, an arcane and endless underground pass… The escapade is unexpected and exciting but turns quickly out to be an adventurous walk and then, when they found out three skeletons trapped behind a door closed from the outside, the worst nightmare ever. The worst is actually still to come since no one knows how to get out of the kind of sphinxlike Underworld (Hell)…

When Nathan releases a thirty years old secret, each one of his friends started to be mysteriously killed by something that appears to be the Grim Reaper…
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I thank yo so much for your help!!
This would make a pretty good book!

A couple of quick pointers for you.

Try simplifying the start a little - During a Saturday afternoon detention, Haly James...

and then bring the reason for detention in at the end - to be the Grim Reaper...all because of some forgotten homework!

This would seem more dramatic to me.

Haley cannot feel 'injustice'.

I also would not describe his friend as a boyfriend. This is reserved for people you are having a relationship with (dating/lovers).

The sphinx is a large statue of a lion with a person's head. I am not sure how tunnels can be 'sphinx-like'.
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Thank you for your help! I'm already correcting my homework and then will give it tomorrow to my teacher....I'll let you know about my grade!!
Hey guys, well I've ma grade......and my grade is.....(suspense) 18/20!!!!! that is so great!!!... that is the best grade I've ever had this year (well, I'm used to having somthing like 16 or 17/20...) So thanks a lot....and see you for my next homework!!
Well done, I'm glad I could help. You obviously work hard to improve so I'm sure you will continue to do well.
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