As a Russian émigré, businessman Samuel Petrukhin (Toby Stephens) is determined to integrate his young family into the establishment. So when Samuel meets the captivating Kathleen Shaw (Keeley Hawes) and her husband Richard (Linus Roache) - a war hero and Member of Parliament - he's dazzled by their upper class glamour. But then MI5 agents blackmail Samuel into spying on the Shaws, and he's drawn into a dark web of deception. These shadowy government operatives could be tempting him into a deadly trap. Are the Shaws really involved in a plot to betray their nation? The country's future is shrouded in doubt. Who can Samuel trust? Anyone?