MI5 discover that an Islamic terrorist is planning to enter the UK and launch an attack. Adam travels to Turkey to infiltrate the route, and seemingly persuades his target to work for MI5. But can they really trust their newest recruit, or is he actually more dangerous than ever before?

When MI5 get information that a terror suspect is coordinating a major attack from his prison cell, they make a shock decision to release him. Harry hopes that he will lead them to the terrorist network behind the attack, but could his high-risk strategy end in disaster?