I have some question/problems, assuming that all the storyline is in this post. (For exemple, the dragon is not a dragon of beauty)
I will start by saying that : If you want to make a simple game, with a simple story, it's cool. :)
But, if your ambition is to give a story a little more original and deep, you have to put more into it.
I guess this post is only a quick description and there is more that you didn't say here. But for the moment, it's kind of too shallow and overused, and boring. Once again, I know this is not the final scenario (I hope so), but with only this much information it's difficult to give good advices. What you wrote is really not sufficient for us (me at least) to help.
It's like there are some good guys who are good because they are the heroes, there is a bad guy because they are bad, there is a traitor because you need a twist, there are characters who are joining because you need more character. Etc... You have to give you character reasons, motivation for doing what they are doing. The other thing I want to note, is there are no links between the action of the character. Why are they goinf to Trenton? And not Fleury-bigoudi?
It can be from the simplest (Lucas join Sheila, because she is so beautiful, and he is so a knight, and duty and derp derp) to more complex (an oracle told him to go find his sister in this village, but by the time he arrives in this village she is dead (illness), but he happen to meet Sheila who looks like her sister, but Lucas was also an agent from a demon who sent him to bring back a random beautiful girl. If he does so, then the demon will grant him power. And he think that the oracle didn't want to show her his sister, but Sheila.)
But not just, he join her because he is part of the hero team.
So now I will start some questions :
Why is Sheila selected? It's random? She is the most beautiful of the clan?
Why Sheila would help a perfect stranger? We need to know more about her personality. Why is she necessary to drive of the ghost? As she predisposition to exorcism, which could explain why she is selected. Because the wise-women of her clan knew that, and she didn't want Sheila to take her place. Or, she love Sheila and knew that with her gift she could defeat the dragon. But as she can't go aganst their clan tradition, she was forced to emprison her, but she indirectly help Sheila to escape.
luck
It's only my personal opinion, but the characters are an important part of the story. You have to tell us more about them! Even if it's just few lines, we have to know about their motivation.
Why Lucas will join her, ok, she helped him, but is this sufficient?
Why Gradly will join them? Imagine the dialog :
Sheila : "Hey, random old guy with an axe, join us in a quest to save my ass by risking yours! There is no reward except for my eternal gratitude!"
Who told them that the dragon can be slain if you break its four heart? It's a well known tradition? Written in book? One of the main character knows it? If the solution is known, why nobody didn't do anything? However, if the dragon is only attacking one remote village and kill one girl each month. Well, it's not so bad.
It could be more interesting if the player fight the dragon a first time, realize it can't be killed the normal way, try to run away. But by doing so Sheila fall into a ruin, and discover a pictures/book/text which tell the story of this dragon, and how to kill it. You could meet Misty who is there because he is in reality a Dragon Guardian whose mission is to protect the dragon. First he want to kill Sheila because she know how to kill the dragon and the location of the 4 hearths . But, as she is the only one to read the text/book or the text/book was destroyed just after Sheila read it. Misty want to know where are the other hearths so he decide to accompany her.
There, Misty could be an interesting character, so let me tell you more about his background. First, you have to know that the dragon, in order to be immortal gave his heart to 4 peopel/monster. And by doing so he gave them a part of his power. Long time ago, as Misty was a young adventurers, he stumble on one of these guardian, and manage to kill him. But he also chose to take the place of the fallen Guardian in order to gain more power. His ultimate goal is to reunite the 4 hearths to have the power of a dragon.
And I'm sorry but : "I join you because a bird told me to!" Is so... silly.
"Phileas, plops downs,", sorry I don't understand. I will assume that the dragon appear near the party.
So a dragon, which is I guess, pretty big, manage to sneak (fly, land(!) and walk) an adventurers party without waking them up? They are sleeping in the open, in an hostile land, and they are not taking turn watching the surrounding or at least be a little cautious? That's a ninja dragon for you.
So, the main point are :
- Add reason/motivation for the characters to do what they are doing. They will be more realistic and loveable by the player.
- Add reason/motivation for the characters to go where they are going. Not because this is the next town on your way.
I will finish my post by saying good luck, I hope all of this will help you a bit :D