Theory:Doctor Who television discontinuity and plot holes/Black Orchid


 * The Mackenzie Trent police box, which the Doctor's TARDIS is disguised as did not exist until 1929, four years after the events of this story, yet the policemen recognise it.
 * Police boxes of a similar design had been put into use starting in 1923; police boxes in general had been in use in Britain since 1891.


 * Just how old is Nyssa? She tries to order an alcoholic beverage but the Doctor cuts her off with a loud cough and stops her.
 * Her actual age in Traken or even Earth years is irrelevant; she appears to be one of "the children" like Adric and as such should act like one in the environment in which they find themselves. Alternatively, perhaps the Doctor knows that vodka (or orange juice) would be harmful to her for some reason. (Nyssa doesn't know what a screwdriver is, she just asks for the same as Tegan.)
 * Nyssa doesn't really know much of Earth (being an alien) and so she just thought it sounded interesting and decided to ask for it.