Merely changing the players is not actually sufficient to make a story unique. In order for the story to be merely similar, it would need to have substantive differences in setting as well as in the actual sequence of events in the story. It's one thing to be inspired by a story and write something influenced by it, but my caution to anyone taking this challenge is that merely copying that Castle story and substituting Bracken will not be permitted here.
If anyone taking this challenge needs or wants clarification, I'm happy to assist. However, the site's Terms of Service is pretty clear.