Sean Travis was a former sonar operation who had served on a few attack subs before being dishonorably discharged. Travis was an eco-terrorist and a member of Joshua Fox's anti sonar group which was dedicated to ensuring that the Navy stopped using sonar waves which were ultimately confusing the whales and eventually resulting in their deaths. As such, Travis sought revenge against the United States Navy. In the meantime, Gibbs and Agent Caitlin Todd arrived on the Philadelphia to interview the five suspects, one of whom they suspected could have murdered the victim and stolen his identity.