S3, E24: Don and Charlie discover a buried secret that will change the FBI team forever, on the third season finale. A mysterious man takes control of a bridge and demands to speak with the Eppes brothers. In the wake of an explosive standoff, the brothers discover the man was a former spy who was poisoned in an effort to keep him from exposing a big secret; he created a master list of spies and traitors from numerous countries and if it's exposed it has the potential to tear apart national security. As Charlie and the FBI try to crack the various codes the spy left behind, they uncover a shocking secret within their own team.