|Series 9, Episode 3|
|Series 09, Episode 03|
|Air Date||4 October 2010|
|Previous||Series 9, Episode 2|
|Next||Series 9, Episode 4|
After a discussion with the Home Secretary Townes (Simon Russell Beale), it becomes clear to Harry that one of the last remaining specimens of a deadly biological agent known as Paroxocybin is stored in Azakstan, a final legacy of the Cold War arms race; the specimen is likely to fall into the hands of a rogue Azakstan nationalist.
A joint MI-5-FSB operation succeeds in seizing the agent, and rendering harmless. However, Azis Aibek (Jonathan Aris), an Azakstan terrorist, learns the whereabouts of the other remaining specimen; it is in London, with the exact whereabouts known to Prof. Kirby (Donald Sumpter), a chemistry professor at a university there. The Home Secretary forces Section D to take FSB officer Viktor Barenshik onto the Grid to help track down Aibek and prevent him from getting hold of the Paroxocybin. While following Aibek across London, it is revealed that one of the original scientists who worked on the agent before its destruction kept a sample.
Aibek figures out that Prof. Kirby's daughter Meg (Amanda Hale) may know where the agent is, and subjects her to water torture to get her to reveal the location. When Lucas, Beth, Dimitri, and Viktor arrive, Aibek flees. But Viktor, with the other members of the team searching for Aibek, continues the torture, and extracts the location from Meg. Viktor kills Meg to prevent her from talking. It is also revealed Viktor wants to take the agent to the Russians in order to justify their invasion of Azakstan.
With his daughter dead, and Viktor having the only knowledge of the location of the Paroxocybin, Harry gets Prof. Kirby to reveal its location to MI-5. Aibek is captured but the capture is kept from Viktor. Section D gives Aibek a deal to trick Viktor, which involves faking a theft of the Paroxocybin. In the aftermath of the faked theft of the biological agent, Viktor kills Aibek; Beth kills Viktor, and Tariq forges a video that makes it seem as if it was Aibek that who killed Viktor and got away from the building. With the Russians thinking that Azakstan nationalists have the Paroxocybin, they withdraw their forces from Azakstan. Meanwhile, Vaughn approaches Lucas asking him for an MI5 file named "Albany".