Back in London after a gruelling operation in Paris, Liz Carlyle has been posted to MI5's counter-espionage desk. Her bosses hope the new position will give her some breathing space, but they haven't counted on the fallout from Putin's incursions into the Ukraine. Discovering that an elusive Russian spy has entered the UK, Liz needs to track him down before he completes his fatal mission - and plunges Britain back into the fraught days of the Cold War.