该剧讲述了Season four of espionage drama "MI-5" finds the team reeling from the loss of Danny (David Oyelowo), but thrown back into action when a bomb detonates near his funeral. Zafar Younis (Raza Jaffrey) and Juliet Shaw (Anna Chancellor) are introduced to the show, in a story involving a potentially devastating terrorist attack in the capital. Later in the season Lyndsay Duncan guest stars as a former MI-5 officer with a deadly grudge, one which threatens the lives of everyone back at The Grid.
