Failure’s Contagious

At Stansted Airport, River follows a suspect while MI5's command room directs the operation. James Webb supplies the man's clothing description, and River moves in. The arrest produces no explosive device. A dispute over the description follows: River insists Webb gave him the wrong colours, while Webb denies it. River then pursues the second man despite orders to stop. He reaches the railway platform, but not soon enough to prevent the suspect activating his device. The apparent catastrophe becomes the training failure hanging over River's career.

His punishment is Slough House, where Jackson Lamb supervises officers who have fallen out of favour. River is handed Robert Hobden's rubbish to search while colleagues trawl unpromising records. The work offers little dignity and no obvious route back to operational duty. Sid Baker, meanwhile, watches Hobden in a café. A spilled drink creates the distraction she needs to copy his USB stick, turning an ordinary encounter into a small surveillance success.

Lamb sends River to deliver the resulting material to Regent's Park. The laptop travels inside a protected flashbox, but River cannot resist finding out what it contains. Opening the box burns his hand; he nevertheless makes his own copy before handing it over. Webb uses their encounter to revive River's humiliation, including the suggestion that his grandfather's influence saved him from dismissal. For River, even an errand becomes another opportunity to prove that he was wronged.

Back at the office, the rubbish points him towards far-right political material. Sid warns him against becoming consumed by the assignment, and Lamb orders them away from unauthorised investigations. Hobden is also alert to the possibility that somebody has been interfering with him. River visits David Cartwright, who explains Hobden's political connections and warns his grandson about the uses to which MI5 can put its discarded staff. River hears a reason to be suspicious, rather than a reason to stop.

The episode also follows lives outside the office. Catherine Standish attends an Alcoholics Anonymous meeting, where thoughts of Charles intrude on the present. Hassan Ahmed leaves a comedy evening with a friend; after they part, he is abducted. That violence changes the scale of the story. Until now, River's frustration has dominated his sense of urgency. Hassan's situation creates a danger that has nothing to do with an officer's wounded professional pride.

The following morning, Roddy Ho establishes that the supposedly valuable copied data is pi. Sid recognises Hobden's decoy, puncturing River's hopes of a discovery. Then footage of Hassan's captivity reaches the team. The captors identify themselves as the Sons of Albion and threaten to kill him at sunrise. River suspects Hobden may connect their dull surveillance job to the kidnapping. Lamb wants the department to stay out of it, but River leaves rather than accept another instruction to do nothing.