I’m grateful to everyone at Hodder for doing what they always do, which is running the best operation in publishing: Anne Perry, Kerry Hood, Jason Bartholomew and all their colleagues. Oliver Johnson steered the book with his usual ineffable genius; and Caroline Johnson scraped off the barnacles with a razor-sharp copy-edit. Jane Conway-Gordon watched my back and muttered dire warnings about polar bears.

For every day working on this book in the Arctic, I spent twenty at home. For those, and all the time in between, I’d like to thank my wife, Emma, for constantly supporting me despite some of my wilder scientific ideas (she has a professional interest in genetics); and my sons Owen and Matthew, for encouraging and distracting me in equal measure. One day, I promise, we’ll go to the North Pole.

All the science in this book is based on actual research. In some cases I may have exaggerated or misappropriated the facts either to serve the story or to simplify complex ideas, or from sheer ignorance. In every case, those distortions are all mine, and no reflection on the real scientists who told me about their work.

For anyone who’s curious, Utgard is located about halfway between Svalbard and Franz Josef Land, and further north, but you won’t find it on any map. Likewise, Zodiac Station combines details of various Arctic and Antarctic bases, but the base, its personnel and its parent organisation are entirely fictional.