Season 3, Episode 1: "Kill Ari Part 1"
After Kate's death, Gibbs vowed to kill Ari Haswari. He wasted no time identifying the terrorist's possible whereabouts. Unfortunately, Haswari was already one step ahead of him. As Ducky examined Kate's corpse, Haswari lurked outside the NCIS building with a sniper rifle, hoping to kill lab technician Abby Sciuto.
With the help of newly-appointed NCIS Director Jennifer Shepard, the NCIS team started to unravel Haswari's tightly bound agenda. But soon they found there was another person they would have to be wary of: Israeli Mossad officer Ziva David, who was sent to convince the team Haswari had not killed Kate. Towards the end of the episode, we saw Ziva on the phone with Haswari, leading us to question which side she was truly helping.
One episode just wasn't enough to answer all the questions from the end of Season 2 ...