Nightshade Crown

This is a short story I had to write for school, and now I im thinking about turning it into a full novel, but I wanted others' opinions on whether it would be worth turning into a full novel.

Here is the blurb-

After saving a wounded stranger in the woods, Esme is dragged to the royal palace and discovers the man she helped is the kingdom's prince. But instead of gratitude, he asks for her help in murdering the king.
Bitter toward the crown and tempted by the promise of a better future, Esme agrees to aid him in secret. As treason unfolds beneath the palace walls, however, she begins to realize the prince's hunger for revenge may be something far darker.
On the night the king dies, Esme discovers the truth too late:
The prince never wanted justice.
He wanted the throne.