The episode also reintroduces Adam Wainwright, now Stewart's husband, as a Labour candidate in a forthcoming parliamentary by-election, though he is played by a new actor (Daniel Weyman, as opposed to Max Brown).
The episode begins with the 16 July 1945 Trinity nuclear test in New Mexico, USA, and is framed within the rising mistrust of the developing Cold War between the West and the Soviets.
Much of this story is loosely based on the real "Tin Eye", Lieutenant Colonel Robin Stephens, who ran Camp 020, an interrogation centre near London during the Second World War.
Women's multi-style coupon buster shoes, fashionable at the time, also serve as a plot point[2] as does Dr Ian Ross' tick-borne tropical disease research.
In August 1944, Mortain – the village with the sunflower farm referred to in the episode – was an important battle site within the wider Normandy Campaign and the eventual allied successes in the Falaise Pocket, but the incident bears similarity with the later Malmedy massacre in Belgium.