NCIS: Season 4, Episode 19

4 - 19: Grace Period

An NCIS team, led by Paula Cassidy, discovers a tip about terrorist activity but it turns out to be a trap, resulting in the death of two agents and Cassidy, grief-stricken begins blaming herself for what happened. Gibbs and his team are sent to investigate the deaths with Cassidy joining them during the investigation. While Ducky is sure that the man who Cassidy received the tip from was dead at least one day before the explosion, Cassidy insists otherwise. At the end, Paula Cassidy dies in an explosion, much to Tony's sadness.