When teenagers who were reported missing are suspected of a series of mass murders in Chicago, the BAU investigates their whereabouts to find a motive for the crimes.
When a 200-year-old medicine jar shatters in a teenager's palm, she is admitted to the hospital with symptoms closely linked to smallpox; House must make a dangerous decision that puts his life in jeopardy; Wilson and Sam comfort a young patient.
The murder of an ex-convict triggers an investigation of his social-climbing sister and her beau, a man posing as a United Nations economist.
Frankie Jr. is brought in to help with a gruesome murder case involving a youth hockey league. Frustrated with Hope (recurring guest star SHARON LAWRENCE), Cailin (recurring guest star EMILEE WALLACE) asks to stay with Maura. But Maura quickly learns that living with her younger half-sister requires skills she does not have.
While investigating a vicious tiger mauling at a New York zoo, the CSIs question the workers at the meatpacking plant the victim owned. Meanwhile, Stella and Dr. Hawkes must solve the murder of a debutante found dead on a Central Park carousel. Also, a new CSI (Anna Belknap) joins the team. (TV-14)