In this paper we introduce an approach to cybersecurity education and helping students develop professional understanding in the form of a Playable Case Study (PCS), a form of educational simulation that draws on affordances of the broader educational simulation genre, case study instruction, and educational Alternate Reality Games (or ARGs). A PCS is an interactive simulation that allows students to "play" through an authentic scenario (case study) as a member of a professional team. We report our findings over a multi-year study of a PCS called Cybermatics, with data from 111 students from two different U.S. universities who interacted with the PCS. Cybermatics increased student understanding about certain key aspects of professional cybersecurity work, improved their confidence in being able to successfully apply certain skills associated with cybersecurity, and increased about half of the students' interest in pursuing a cybersecurity career. Students also reported a number of reasons why their perceptions changed in these areas (both positive and negative). We also discuss design tensions we experienced in our process that might be encountered by others when creating simulations like a PCS, as they attempt to balance the authenticity of designed learning experiences while also sufficiently scaffolding them for newcomers who have little background in a discipline.