The episode ends on a literal and metaphorical cliffhanger, leaving the fate of the team and the city of London hanging in the balance.
: The mousy housewife Alex Tropper is revealed as a highly capable Russian "cicada" sleeper agent. After stunning a captive River Cartwright, she takes to the skies in a plane loaded with explosives, headed for London's Glasshouse. Slow Horses 2x5
: A frantic River eventually escapes his bonds and calls in a "Code September" alert, triggering a city-wide shutdown and mass evacuation that MI5's Diana Taverner must manage amidst a backdrop of anti-capitalist protests. The episode ends on a literal and metaphorical
: While the city panics, Jackson Lamb (Gary Oldman) diggs into the MI5 archives. He discovers his own signature forged on defection papers, leading him to realize that the unassuming Nikolai Katinsky is actually the Russian spymaster pulling all the strings. : A frantic River eventually escapes his bonds
As the penultimate chapter of the season (based on Mick Herron's Dead Lions ), this episode maneuvers every Slough House agent into place for a race against the clock.
: The tension peaks in the eponymous boardroom where James Webb’s meeting with the Russian Pashkin goes south. Ignoring the evacuation sirens, Webb is shot by Pashkin, leaving Marcus and Louisa trapped in a room with a dying man and an escaped assassin as the episode cuts to black.
: Catherine Standish proves her worth in a high-stakes chess match against Victor Krymov. Her victory secures the intelligence Lamb needs to confirm Katinsky is specifically targeting Slough House.