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InseasonsixoftheBritishespionagethriller,theteamarepushedtotheirlimits,astherelationshipbetweenBritishandAmericansecuritydeterioratesandloyaltieschange.AdamandRosfightagainstanemergingterroristthreat,andadeadlyvirusthatcoulddecimateLondon.Thisseasonbreaksawayfromthecase-by-caseepisodicformat,withonedominantstorylinetyingalltheactiontogether.