When a man enters an office in Boston for a meeting, he becomes disoriented and collapses, only to have his veins erupt and spray blood everywhere. Shortly after Olivia and Peter arrive at the scene to investigate the bizarre case, it’s discovered that a lethal virus with deep ties to something very valuable is spreading, so the CDC moves in to quarantine the building and eradicate the pathogens. Isolated inside with the rest of the exposed office employees, Peter and Olivia face life-threatening circumstances, sending Walter, Broyles and Astrid on a frantic search for a solution to save them.

While investigating the death of an Irish mobster, Beckett and Castle uncover a local turf war that may be connected to both a late-night infomercial guru and an international drug smuggling operation. But the case turns agonizingly personal when evidence emerges that the killer they’re chasing may have had a hand in Beckett’s mother’s murder.

When Lily refuses to believe that Jenkins, Marshall’s attractive female colleague, kissed him, Marshall insists Jenkins tell Lily what really happened. Meanwhile, Robin finds out that a drinking game has been made up about her.

Hiros life hangs in the balance as his brain tumor worsens, prompting him to subconsciously deal with some of his past decisions. Meanwhile, Sylar pays Claire an unexpected visit to get answers as to why he isn’t quite himself. Elsewhere, Samuels plan to impress his long-lost love, Vanessa, takes a terrifying turn.

Jack and Chloe race against time to try to thwart a well-planned assassination of the President of the Islamic Republic.

A plot to assassinate the President of the Islamic Republic at the UN building comes to Jack Bauer’s attention.