In this paper, we propose a computational framework for automated story-based scenario generation. Under this framework, a regular grammar is developed to model various causal relationships inside a given story world. The grammar is then evolved using evolutionary computation techniques to generate novel story plots, i.e. story-based scenarios. To evaluate these newly generated scenarios, a human-in-the-loop model is used. An experimental study was carried out, in which the proposed framework was used to create novel plots based on the famous Little Red Riding Hood fairy tale. The experimental study demonstrated that evolutionary computation can potentially contribute significantly to story generations. Some challenges were identified including the difficulty to quantify such subjective measures as plot interestingness and creativity.