Season 4, Episode 4:
MI5 is alerted to information that a high profile terrorist belonging to a new Islamic splinter group, plan to enter the UK via an illegal immigrants truck. MI5 send Adam and Zaf to Istanbul where they infiltrate the truck and on the journey attempt to turn the terrorists away from his militant ideals. They succeed, but Adam and Zaf are not wholly convinced by the transformation. Back in the UK the team must decide whether to trust the terrorist and risk serious consequences. Too late they realise the terrorist's true game and it yields disastrous consequences.
Missed this one? Trying to catch up? Read our recap of this episode here.