Drama series about the British Security Service. As the team discover the size and reach of the Yalta organisation, Ros desperately attempts to escape identification. However, her betrayal is revealed by Ben Kaplan. Knowing her very limited options, she presents the furious Adam and Harry with a proposal - if they permit her to head to the Yalta headquarters, she will be in a unique position to infiltrate and disembowel Yalta's grand plan. But can she be trusted?