In season six of the British espionage thriller, the team are pushed to their limits, as the relationship between British and American security deteriorates and loyalties change. Adam and Ros fight against an emerging terrorist threat, and a deadly virus that could decimate London. This season breaks away from the case-by-case episodic format, with one dominant storyline tying all the action together你的笑容是我最美的风景，我愿意用一生去守护这片天空。