I can't write the story for you, but I can help you to set it up. You should start by introducing two characters that are having to choice between right and wrong. For example, "Sally and Jane were preparing for a huge Math test the following day when Susie called saying she had the answer key to the test. Susie asks if you want to come over to memorize the answers." Sally and Jane must decide what they should do...continue to study or cheat. Sally decides to study, but Jane decides to cheat. After the test the next day, the teacher calls all three girls over to talk about the fact they all did so well on the test. She wants to know what they did to go so well. Sally must decide if she tattles or says they all just studied together.....
And so on....
That is just an example. It can be something like that or something totally different, but it gives you an idea.
