Tom Billett

Bosco and his agents are gunned down within the walls of CBI headquarters. With two men dead and Bosco in a critical condition, Lisbon and her team race to find the perpetrator. As the investigation progresses, it becomes clear that notorious serial killer Red John is responsible - and he has an assistant inside the department.

A scientist is deliberately exposed to a deadly toxin at a high-security biological research facility. Before she dies, she calls Jane to ask for his help in finding her killer. Once the agents have arrived on scene, however, another empty flask of the toxin is discovered, suggesting all those inside the facility have just hours to live.

Alison puts on a brave face as she returns to Rosewood High and attempts to repair the damage she inflicted years earlier; Caleb and an old nemesis return.

An undercover operation targeting drug smugglers goes wrong, and Boston PD's homicide HQ is next in the gang's firing line.

As the Cohens prepare for Kirsten's 40th birthday party, Kirsten gets some news that will change her life forever. Meanwhile, Julie is having a secret love affair and Kaitlin is doing everything she can to stop it. Elsewhere, while Ryan acts as if he doesn't miss Taylor, she visits a therapist who gives her some rules to live by, and Seth and Che's plan to save Newport's groundhog goes awry.