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...
Elenco: David McCallum , Mark Harmon , Sean Murray , Pauley Perrette , Brian Dietzen , Michael Weatherly , Rocky Carroll , Cote de Pablo , Emily Wickersham , Wilmer Valderrama , Maria Bello , Duane Henry , Sasha Alexander , Jennifer Esposito , Tim Kelleher , Diona Reasonover .