Following a gruelling operation in Paris, Liz Carlyle's bosses post her to MI5's counter-espionage desk, but they haven't counted on the fallout from Putin's incursions into the Ukraine. Liz needs to track down a Russian spy who has entered the UK before he completes his fatal mission. Meanwhile, the intelligence services are in the spotlight. In response to the debate raging around privacy and security, they hire Jasminder Kapoor, a controversial civil rights lawyer, to explain the issues to the public. But in this new world of shadowy motives and secret identities, Jasminder must be extra-careful about whom she can trust.