The critical acclaim has strengthened with each season. According to Rotten Tomatoes, Season 2 holds a 98% critics' score, Season 3 returned to a perfect 100%, and Season 4 maintains a 95% score. All four seasons hold a Certified Fresh rating, with two seasons achieving the rare, perfect critics' score.
River and agent Sid Baker begin investigating a journalist; a kidnapping of a student, Hassan Ahmed, is announced.
As the team investigates, they uncover a "false flag" operation orchestrated within MI5 itself to manipulate public image and political figures. Episode Guide Failure's Contagious
The TV show remains remarkably faithful to the source material. However, some changes were implemented to enhance the story: