The work of a historian is never done. The very nature of history ensures that this is so. Past events are not frozen in time. Evidence pertaining to them is never complete, hardly ever incontrovertible, and so capable of often sharply contrasting interpretations. Rooted in the present, the historian watches the object of his studies recede, steadily and ineluctably. All he can do is to dig further, probe more widely and ask different, yet more searching questions to retrieve a little more of the past, its complex and changing contexts, always knowing that, ultimately, it will elude his grasp. When discussing such matters, Keith Neilson was fond of quoting Günter Grass, the German novelist, who in his memoir of his own uncertain past likened interrogating it to peeling an onion. He argued ‘that “when pestered with questions, memory is like an onion that wishes to be peeled so we can read what is laid bare letter by letter. It is seldom unambiguous and often in mirror-writing or otherwise disguised.”’ Keith thought ‘that we should take this advice to heart and continue to peel the onion’.

Sometimes, however, the work is left undone because, more prosaically and yet more cruelly, the life of the historian is cut short just at the moment when his latest work nears completion. This is also the case with The Foreign Office's War, 1939–41, which Keith left behind, when he died in April 2015, shortly after retiring as Professor of History at the Royal Military College of Canada (Collège militaire royal du Canada) (RMC). He had devoted much of his life to the study of great power politics, and more especially the British Foreign Office and the service departments in Whitehall, the mores and mentalities of diplomats, officials and their political masters with particular reference to their dealings with Russia, both in her Tsarist and her Soviet guises.

Historians bring to their work a distinct perspective, reflecting their own background and upbringing and conditioned by their generational experiences.