 In the meantime, they also try to find out who killed two off-duty sailors whose deaths might be linked to an upcoming terrorist attack and the theft of a drone from a company.But in the end, it might not be enough as NCIS find themselves paying a very high price for their efforts when one of their own is brutally murdered in Gibbs and Ari's battle with each other...The episode also marks the final regular appearance of Special Agent Kate Todd (played by Sasha Alexander), who is later replaced by Mossad Officer Ziva David (played by Cote de Pablo).