Andrei Vassilov, unaeded [sic] and alone in the snowy night, had to get inside those forbidding and forbidden walls. Past the guards, and that death dealing electronic fence, across the mine field and the icy moat with its poison spikes, and into the castle itself. Even if he got inside the awesome fortress, could he hope to get out alive?

Extract found on line for The Secret Circle: Operation Royal Family, published 1974. The castle is in northern England, and holds the secret of Adolf Hitler’s true relationship with the British royals. And no, Andrei doesn’t get out alive. I lost my copy many years ago; I occasionally look out for a new one, but it’s not a priority.