Most girls dream of becoming a princess, but Nadine is not most girls. When King Joseph informs her she has been chosen to marry the ruthless prince of Embero, she does the only thing any self-respecting girl would do: She runs.
-Why is Nadine not most girls? Give some characteristics.
-Is King Joseph her father?
-A little more charactization of Nadine
-A little more background of the kingdom. What are its characteristics?
During her flight, seventeen-year-old Nadine is summoned by the White Witch Evangeline. Nadine reluctantly accepts the task of protecting the Rebellion’s greatest treasure, the Last Dragon, against the bloodthirsty armies of Embero. Aided by an aspiring soldier and his sister, Nadine begins her perilous journey across the world of Earthea to join the Rebellion.
-Seventeen-year-old should be moved up to the first paragraph.
-What do you mean she is "summoned"? How was she located if she's on the run? Was she bumped into? Did an owl come by carrying a letter? Give specifics
-The Rebellion? What's the rebellion? If you need to give some backstory, go ahead and give it. I might say something like "The Rebellion is blah-blah-blah against the king, and they task Nadine with protecting their greatest treasure." Be sure and give the connections between Evangeline, the rebellion, the Last Dragon, and Nadine.
-Is the Last Dragon an actual dragon? It's capitalized like an item might be.
-Why does Nadine accept the responsibility of the Last Dragon? What's at stake? What's to lose and what's to gain?
-Name the soldier and sister, since they appear to be significant.
-I would by more "synopsis"-y here. The summary is too general. I want to see how Evangeline contacts Nadine, what motivates her to take the task.
As Nadine gets better acquainted with the dragon, she discovers that he has a human soul and falls in love with him. She dreams of a future with the man behind the beast--if they can survive that long.
-Take out the second sentence. It is not the story.
-I might use something different than "better acquainted"
-BTW, why does Joseph want Nadine to marry a man from a kingdom full of "bloodthirsty" armies?
Nadine’s love for the dragon is rivaled in intensity only by King Joseph’s fear of death. He burns a path across the world of men to obtain the dragon’s golden vein--a filament in the dragon’s heart--that has the power to grant its consumer immortality.
-Take out the first sentence. It is not the story.
-I'd combine this with the above paragraph. This is the stakes, or at least some of them.
Directed by his father, Prince Kellan is given the singular task of capturing the girl and the dragon she loves. But the prince has secrets and aspirations of his own: by day he may be his father’s right hand man, but by night he accompanies Nadine in the form of the Last Dragon.
-Prince Kellan? Who? The fourth paragraph is not the time to introduce new characters.
-Who's his father?
-This doesn't make sense. It sounds like Kellan is in two places at once: pursuing Nadine and then he's right by her side.
I think you need to restructure your query from scratch. One of the bigger problems is that I don't get a sense of your voice in your query. It sounds like you're disinterested in your own novel. You gotta puff the story up. Bring in the drama, the excitement, the puffery. It's okay to get a little cheesy.
Another problem is that you only offer a summary of the story. I don't know the word count or genre, nor your other credits (though you may have not listed them here for the purposes of revision, in which case, ignore this comment)
But your summary leaves a lot to be desired. I think the story could be interesting as a fantasy romance, but right now it sounds so generic and general, I don't see any reason to pick it up. What makes your story different? And especially focus on the dragon. That's the most attention-getting piece.
I suggest to you a website:
http://queryshark.blogspot.com/. Read all the entries on this page and familiarize yourself with query letter structure, along with what to do and not to do in a query.