After a young woman's baby is tossed out of a car, Benson and Stabler investigate to find out what happened, and after learning the young woman is addicted to prescription pain killers, their investigation leads them to an elderly woman named Jenny Rogers, who lives with her son Kevin and daughter-in-law Carol. The young woman finally identifies Carol Rogers as the person who solds her the drugs, but when detectives go to confront Carol they find her body, and are left trying to uncover who really killed Carol.
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. Tony's health gets worse.