When a concert in the park turns violent and the NYPD are forced to break up the fight, a young female winds up dead in the process. As Sid is pressured to determine C.O.D., he suddenly becomes ill and has to be hospitalized.
Following the incident, the CSIs learn the victim's death was actually caused by lethal exposure to radiation, contaminating Sid in the process and forcing the lab to initiate CDC protocols. The CSIs ultimately find the source: a book from the New York City Library Antiquities Branch with pages stained by high volumes of Thallium 201, causing death by contact. The story takes yet another turn when the husband of a deceased librarian files suit against the city, believing her death was also caused by radiation poisoning.
But when his story doesn't add up, the CSI have to determine if he was the real mastermind behind the murders.