Also, the "Th" could be part of a longer phrase, maybe "The Halloween Switch" or "The TWIN Switch". Maybe the story ends with a cliffhanger or sets up for a sequel if the ... at the end implies continuation.

Conflict: When sisters swap places, classic problems arise like dealing with their different responsibilities, friends, or family. Maybe they can't switch back immediately, so they have to figure out how to handle their respective situations. Maybe there's a reason they wanted to switch in the first place, like one wanted to attend a friend's party and the other had a study group. Or perhaps they were curious about each other's lives.

Themes: The story could explore understanding each other's perspectives, learning empathy, dealing with challenges beyond their experience. Maybe they realize how the other person struggles or has strengths they hadn't noticed before.

Conflict resolution: The swap leads to them understanding each other better. Maybe they find out that they're both under stress in different ways, and the experience helps them support each other.

As dawn breaks, the medallion glows one last time, sinking into the river. A mysterious ripple suggests the sisters swapped more than just bodies that night… To be continued?

I think that's a good start. Let me outline the story with these elements in mind.