This case study used individual interviews to investigate graduate students' sensemaking in upper-level electrostatics in the context of problems that can be efficiently solved for the electric potential using Laplace's equation. Although there are many technical mathematical issues involved in solving Laplace's equation, the focus of this research is not on those issues. Instead, the focus is on structural issues such as whether students recognize when solving Laplace's equation would be an effective approach to finding the potential and set up the problems correctly, and whether they can draw the electric field lines and equipotential surfaces in a given situation. Although many prior investigations have shed light on student sensemaking in introductory physics contexts, very few investigations have focused on graduate student sensemaking while solving advanced physics problems. We present the findings of our research, which was conducted through the lens of the epistemic game framework proposed by Tuminaro and Redish. We observe different nested epistemic games played by students.