The tense spy drama continues as the team learns that the Azakstan Freedom Front (AFF) are searching for a deadly nerve agent called Paroxocybin. Harry (Peter Firth) sends Lucas (Richard Armitage) to join forces with the Russians to help stop them before it’s too late.

Lucas and FSB officer Victor Barenshik (Julian Lewis Jones) manage to destroy the sample but are shocked when the Russians mercilessly kill the AFF members. Back in London, Section D find out a member of the AFF, Aibek, has survived. Harry makes a controversial decision to let him run but is forced to take drastic action once he finds out Aibek is on his way to London in search of a second sample of the nerve agent, held by British scientist Stephen Kirby (Donald Sumpter).

Lucas, Beth Bailey (Sophia Myles) and Victor follow Aibek’s trail through London, desperate to get to him before he finds the Paroxocybin, however Victor exposes his own more sinister motives for getting hold of the nerve gas.

With time running out, the team has to work quickly before London falls victim to a biological weapon with that, if it were to be released, would have catastrophic consequences.