I need someone to help me with ideas on a story

I'm going to write a story. I couldn't find one like it, so I decided to make one myself.
It's Sweeney Todd, version 2.0
I'm using the same characters, beginning, and ending, I just want to change things around.

It starts with Sweeney on the boat with Anthony, and ends with the same shot in the movie.
But, I'm changing around the rest of the plot.

I've got ideas for it, but all of them won't work together. I want someone to help me narrow down my options and help me come up with new ones.
I will give credit to said person in the summery of the story.

Please you guys, I need help with this.

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