The year is 1972, the Cold War is far from over and Serena Frome, in her final year at Cambridge, is being groomed for MI5. Sent on Operation Sweet Tooth – a highly secret undercover mission – she meets Tom Haley, a promising young writer. To answer these questions, Serena must abandon the first rule of espionage – trust no one.

It is July 1962. Edward and Florence, young innocents married that morning, arrive at a hotel on the Dorset coast. At dinner in their rooms they struggle to suppress their private fears of the wedding night to come...