When Tony opens a mysterious letter thinking it's for him, a small puff of white powder comes out and it releases a possible deadly virus. Kate calls for help and soon she and Tony are isolated in a bio-hazard isolation room for precausion. McGee and Gibbs work to discover who sent the envelope and how to cure their friends before its too late for them. Meanwhile, Tony's health gets worse...

The NCIS team must protect Ziva when a suspect dies while being in custody, and her tactic might be the reason why the person died. The things become much more dangerous when the suspect's brother kidnapps Jenny, and demands the release of his brother in exchange for Jenny, but he has no idea that his brother is dead.