SLOW HORSES, S3 We know the drill by now. Each season of 'Slow Horses' begins with a big, pulsating set piece. But this time around it's not occurring in Blighty but in Istanbul where Sope Dirisu's head of security at the UK Embassy Sean Donovan is spying on Katherine Waterston's MI5 agent Alison Dunn. She is suspected of trying to leak information that could be highly damaging to British intelligence. The only problem is Sean and Alison are also lovers and when she discovers he is spying on her a cat and mouse game around Istanbul ensues as he tries to intercept a stolen document she is going to pass on to a mystery man. Losing him during the chase at dusk, Sean eventually catches up with where she is at an empty football stadium, only to discover Alison has been thrown off the building. A year later, Sean resurfaces in London at an AA meeting that Saskia Reeves' Slough House office administrator Catherine Standish attends regularly. Posing as an alcoholic name...