An attack on the Da'Kel system using a banned isolytic explosive destroys the station co-coordinating the Federation's relief effort with the Klingons. The Federation insist on participating in the investigation and the Excelsior is assigned as an observer. Lieutenant Elias Vaughn, a junior officer of Starfleet Intelligence finds evidence suggesting a link between the attack and the assassination of Chancellor Gorkon and, when he fails to convince his superior, takes the information directly to Sulu and Darius Miller, the Intelligence officer handling the case. He ends up being invited to join them on the mission.