Active learning is an engaging way of teaching and even experienced professors may not know how to start implementing its techniques to make classes more dynamic. Teaching cases can be a very useful active method of instruction, as an opportunity to assign students roles in the case discussion, centering them as the protagonists of their own learning process. In other words, students will learn by doing, as they will be engaged in thinking and communicating on the topic. This paper presents a teaching case on the Brexit process to introduce central concepts of Putnam's Two-Level Game model, such as level of negotiations, chief negotiator, win-set, voluntary defection, involuntary defection, and ratification. We assessed learning with self-perception questionnaires before and after the activity. The results suggest the activity improved the understanding of all selected topics covered in class.