The pressure is on for Beth when she goes undercover for MI5 for the first time. She is tasked with protecting an influential oil baron, Robert Westhouse, when the team receives intel that an assassination attempt will be made on him at a meeting of top oil dealers. But an unexpected ambush throws things off course, and threatens to dredge up her murky mercenary past. Meanwhile, Lucas visits someone who never expected they would see him again.

Section D is forced to welcome an FSB officer onto the Grid to help track down Aibek, a rogue nationalist from the ex-Soviet state of Azakstan. Aibek is in the UK to find the last known sample of the nerve agent 'Paroxocybin'. The chase is on, but will the team find a way to stop the nerve agent falling into the wrong hands without ruining Anglo-Russian relations? Meanwhile, Lucas's personal life takes a passionate turn.