Write a short story in the point of view of an unreliable narrator who witnesses or experiences something wrong and makes the decision of whether or not to speak up. Show in your story how the narrator speaks up or refrains from speaking up, and why. Show the consequences his/her/its actions have on the plot.
Keep in mind that an unreliable narrator does not necessarily have to be someone who is not sane. Your narrator can be a young child, an unhappy teenager, a superstar, a pseudo-scientist, a doting mother, an overprotective father, a zealot, a prisoner, a jealous lover, a troubled neighbor, a powerful person, a rich person, etc. It can even be an animal (e.g., your pet), a plant, or even an inanimate object. Feel free to be creative and define in your own way who an unreliable narrator is.
While writing your short story, you may find it helpful to refer to Chapter 8 in Knowing Language.