Every day, Britain's Secret Intelligence Services are fighting an invisible war against a multitude of hidden threats. In this series, three former spies put 15 men and women to the test to see if they have the skills and qualities required for that battle. Halfway through the course, 10 trainees remain. Control must use a series of exercises to decide who they'll take on the course's final overseas challenge: a brutal decision they'll be forced to make shortly. Among the exercises is one of the most notorious in spy training. Control tell the trainees to enter a pub and - with nothing but their own guile and imagination - extract key intelligence from unwitting strangers. Roopi impresses with her natural performance, but Lisa and Hugo almost blow their cover, and serious questions are raised about Rohan. In another exercise Control bring in two former detectives to challenge the trainees' ability to defend their cover, but one of them falls at the first hurdle.