|Series 8, Episode 4|
|Series 08, Episode 04|
|Air Date||20 November 2009|
|Previous||Series 8, Episode 3|
|Next||Series 8, Episode 5|
Lucas's interrogator/torturer, Darshavin (Emil Hostina), escapes from a British immigration centre and demands to speak with Lucas regarding an attack planned by Sudanese terrorists with the complicity of the FSB. They meet at a location in the Thames estuary, and Darshavin informs Lucas about the attack without giving away much detail. Darshavn demands a British passport under an assumed name and $1 million in unmarked bills in exchange for information on the exact location and the plotters.
Harry displays doubts, believing Lucas developed Stockholm Syndrome from his capture. Samuel Walker (Brian Protheroe), Sarah Caulfield's (Genevieve O'Reilly) CIA boss, orders her to continue her affair with Lucas in order to continue to try to get information from the MI-5 operative. Lucas goes off-track to get the target, meeting with Darshavin again, this time at Lucas's flat, but fails to get more information when Lucas's paramour Sarah interrupts. After Darshavin leaves, he hides in Sarah's car, and abducts her as she phones Walker to convey what she knows from Lucas.
Tariq and Ruth discover the location of the bombs from an asset who fled his home base out of fear but left a clue on the Web. Harry learns that Darshavin let a Sudanese terrorist go when interrogating the terrorist back in Russia, only to join the terrorist plot and escape Russia. Ros track one of the terrorists to an apartment over a bar but the terrorist is killed by his own men, who then escape. Lucas negotiates with Darshavin and extracts the trigger code from him—for Darshavin wants the money and the new identity more than anything else--, relaying the information to Ros who disarms the explosives on site.
In the end, Darshavin, sitting in a car with Lucas waiting for agents to show up, tells Lucas that there was recently a secret meeting in Basel attended by rogue Western intelligence agents and agents from China. A car shows up; it is the FSB—not MI-5—to haul Darshavn back to Russia. Sarah reveals herself to be part of "Nightingale", by throwing Walker over a railing to his death 100s of feet below.