Bayesian networks have gained popularity as a probabilistic tool for reasoning with legal evidence. However, two common difficulties are (1) the construction and (2) the understanding of a network. In previous work, we proposed to use narrative tools and in particular scenario schemes to assist the construction and the understanding of Bayesian networks for legal cases. We proposed a construction method and a reporting format for explaining or understanding the network. The quality of a scenario, which plays an important role in the narrative approach to evidential reasoning, was not yet included in this method. In this paper, we provide a discussion of what constitutes the quality of a scenario, in terms of the narrative concepts of completeness, consistency and plausibility. We propose a probabilistic interpretation of these concepts, and show how they can be incorporated in our previously proposed method. We also illustrate with an example how these concepts concerning scenario quality can be used to explain or understand a Bayesian network.